I found the following post on DefenseReview.com concerning a new 6.8mm cartridge based on a .223/5.56 case expanded to accept 6.8mm bullets.  Claimed performance is equal to a 6.8 SPC but only requires a new barrel, and modified mags will hold 20 or 30 rds just like the .223/5.56.  I'm interested in this concept because it uses existing .223/5.56 brass and you can easily modify PMags to hold this round while still maintaining their full functionality with .223 ammo.

19 June 2008  By David Crane

DefenseReview has covered the 6.8 SPC round for quite some time now. We're a proponent of the cartridge, due to its superior efficacy over /.223 Rem. / 5.56x45mm NATO within its (6.8 SPC) operational envelope of 400-500 yards, its grassroots-level development history, and the support it's garnered inside the U.S. Army Special Forces (SF) community and general SOCOM/Special Operations (SPECOPS) community.

Developed by elements within U.S. Army 5th Special Forces Group (with help from private industry like Precision Reflex, Inc., Remington Ammunition, Hornady Manufacturing, etc.) in order to achieve significantly-enhanced terminal ballistics over 5.56mm NATO for close quarters battle (CQB) and short-to-medium-distance engagements, the 6.8 SPC's total development cost was approx. $5,000. This is according to one of the SF developers, who's a contact of ours. Understand that the 6.8mm SPC cartridge was developed totally outside the normal U.S. military small arms and ammunition development and procurement process that's currently ruled over by the U.S. Army Infantry Board Fort Benning, GA, Picatinny Arsenal/JSSAP (Joint Service Small Arms Program), and Naval Surface Warfare Center (NSWC), Crane Division. Because of this, the 6.8 SPC has been met with considerable resistance from the U.S. Army hierarchy, putting the cartridge's future in jeopardy.

In Defense Review's experience so far, any/all SF/SpecOps assaulters/operators that have been highly supportive of the cartridge. We recently heard that U.S. Marine Corps (USMC) Forces Special Operations Command (MARSOC) assaulters/operators want 6.8 SPC HK416 carbines and SBR/subcarbines. Heckler & Koch has reportedly already built prototype HK416s in 6.8 SPC. Speaking of (or, in this case, writing about) gas piston/op-rod-driven AR carbines and subcarbines/SBRs, Land Warfare Resources Corporation (LWRC) has a sweet little 8" M6A2 CQB-type SBR/subcarbine on which DefRev published information awhile back.

One of our contacts in 5th group told us that when he and his unit have been in combat, they feel under-gunned/under-powered with 5.56mm weapons, and he's notices that the operators carrying 7.62x51mm NATO (7.62mm NATO)/.308 Win. M14/M1A rifle/carbines carry themselves very differently than their 5.56mm AR-carrying counterparts. M14/M1A gunners, in his experience, are generally more confident and aggressive in combat. The larger round gives them not only an combat-operational edge, but also a psychological one. This, of course, was one of the reasons why he wanted to develop a larger-caliber, harder-hitting assault rifle cartridge like the 6.8mm SPC that essentially splits the difference power-factor and size-wise between the 5.56mm NATO and 7.62mm NATO cartridges.

To utilize 6.8 SPC in his AR carbine or SBR/subcarbine (AR-15/M16, M4/M4A1, Mk18 MOD 0 CQBR, HK416, etc.), the operator can either employ a dedicated 6.8 upper receiver or convert their existing 5.56 AR upper by swapping out the barrel, bolt, and magazine to 6.8 SPC versions, and they're off and running and gunning. Larger M4/M4A1 feedramp cuts can also be cut. The same AR-15 lower receiver is used.

Well, now there's a new 6.8mm assault rifle cartridge being made by Kramer Defense (KD), a Division of Kramer Cartridge & Carbine LLC (KCC), that gives approximately the same or similar performance as the 6.8 SPC without having to go to a modified .30 Remington case. It's called the 6.8x45mm Kramer Urban Combat Cartridge (UCC) a.k.a. 6.8mm Kramer UCC a.k.a. 6.8 Kramer UCC and it utilizes a standard 5.56x45mm NATO cartridge case. DefenseReview first became aware of the 6.8 Kramer cartridge at SHOT Show 2008 when we ran into Larry Kramer in the tents outside of Oakley Eyewear's booth. Mr. Kramer handed us an inert round, and explained to us that he could safely achieve roughly the same velocity as the 6.8 SPC, which surprised us. Kramer claims that he can safely get a 115-grain (115gr) Hornady OTM 6.8x45mm Kramer UCC bullet up to 2500 fps (feet per second) out of a 16" 1/11-twist Krieger barrel, and has done so in tests. Kramer's firing test results comparing the 115gr OTM 6.8mm Kramer cartridge to 62gr SS109/M855 ball 5.56mm NATO and 123gr 7.62x39mm Russian ball are below. Kramer achieved 2440 fps out of a 14.5" Krieger barrel with the same Hornady 6.8 OTM round.

About a year and a half ago, Kramer was averaging 2550 fps out of a Precision Reflex, Inc. (PRI) 6.8SPC AR upper with Silver State Armory (SSA) ammo utilizing a 115gr Remington FMJ boattail round. In a recent article that Kramer read in Guns & Ammo Book of the AR-15, titled "Barrett's REC7 Battle Rifle", author David Kenik got 2500 fps out of a 16"-barreled 6.8 SPC Barrett REC7 gas piston/op-rod-driven carbine with SSA ammo utilizing a 115gr Sierra OTM bullet, so SSA might have down-loaded the cartridge since Kramer tested it (unverified/unconfirmed). In any case, Kramer is achieving comparable velocities to 6.8x43mm SPC with the 6.8x45mm Kramer.

We should perhaps note that we ran into one of the SSA guys at the Land Warfare Resources Corporation (LWRC) booth at SHOT Show 2008, and he was very friendly and helpful with information about the 6.8mm SPC ammo they're manufacturing. SSA was sharing LWRC's booth space. DefenseReview has heard some very good things about SSA's 6.8 SPC ammo, lately.

So, why go to 6.8x45mm Kramer UCC instead of 6.8x43mm SPC? Well, first, you get comparable muzzle velocity and energy. And, since the 6.8 Kramer UCC utilizes a standard 5.56mm NATO cartridge case, you only have to change out the barrel and mags on your AR. Unlike the 6.8x43mm SPC, you don't have to swap out the bolt. Regarding standard 5.56mm NATO AR-15/M16 mags, according to Kramer, MagPul PMags can be modified easily to feed the 6.8 Kramer reliably, and once the mag is modified, it will still feed 5.56x45mm NATO ammo just as reliably as before the modification. Kramer is going to have aluminum mags made for his cartridge. With the 6.8 Kramer UCC cartridge, you should also be able to use Mil-Spec M249 Squad Automatic Weapon (SAW) ammo links, meaning that the 6.8x45mm should be able to be fired from a FN M249 SAW/LMG or FN Mk46 MOD 1 LMG/SAW by simply swapping out the barrel, which is a relatively minimal modification. Bottom line, you only have to swap out the barrel of your assault carbine/SBR (M4/M4A1 Carbine, Mk18 CQBR MOD0 SBR/subcarbine, or HK416 Carbine or SBR) or LMG/SAW (FN M249 SAW or Mk46 MOD1), and swap out your AR mags. Mr. Kramer points out that you can use standard 5.56mm stripper clips, bandoliers, and U.S. military ammo storage cans. 6.8 Kramer adds 5.75 lbs to a U.S. military standard 840-round 5.56x45mm ammo storage can.



If you want to read the whole thing, Here is a link to the article including a long discussion of the development progress by Kramer.

Sounds like the .270 Ingram, circa 1979

15" Barrel with Hornady 110gr HP Spitzer

Using H-335, H-322, and RE-7 powder.

2,290fps to 2,450 fps Muzzle Velocity.

New?  Hardly.

I'm suprised it would need different mags. Both the 6.5mpc and 7.62x40 (223 case with 30 pill) utilize the standard 223 magazines, don't they? Why would this cartridge be different?

That is what I was looking for with my 6.8x43/17rem.It looks like he was about a yr -yr1/2 ahead of me.It looks like he has a better shoulder solution though as the shoulder height is about the same as the 223.I like it , now maybe I won't have to pay quite as much for reamer or dies.

Quoted: Sounds like the .270 Ingram, circa 1979 15" Barrel with Hornady 110gr HP Spitzer Using H-335, H-322, and RE-7 powder. 2,290fps to 2,450 fps Muzzle Velocity. New?  Hardly.

Cartridge dimensions the same?

so what about terminal ballistics? A .224 dia m855 doesn't just punch a .224" hole, it frags. I'm guessing that this bullet will just punch a .270 diameter hole. Theres probably not enough energy to make it frag.

Jon

Quoted: So what about terminal ballistics? A .224 dia m855 doesn't just punch a .224" hole, it frags. I'm guessing that this bullet will just punch a .270 diameter hole. Theres probably not enough energy to make it frag.

I believe Gary Roberts has stated certain 6.8 bullets will fragment reliably down to 2100 fps.

My question: The photo shows the 6.8 loaded longer than the 5.56. Does that mean it's too long for mag length?

John

| 6.5 Grendel: The State-of-the-Art Combat Cartridge. |

www.65grendel.com

Yawn

Quoted: so what about terminal ballistics? A .224 dia m855 doesn't just punch a .224" hole, it frags. I'm guessing that this bullet will just punch a .270 diameter hole. Theres probably not enough energy to make it frag. Jon

I don't know about fragmentation, but most of the 6.8 stuff I've read says that it has good expansion out til about 1900 fps or better .Which ,would make this cartridge good out to about 250 yds.And still carrying almost 1000ft/lbs @ 300.That's going by Kramer's info though.

Quoted: Quoted: So what about terminal ballistics? A .224 dia m855 doesn't just punch a .224" hole, it frags. I'm guessing that this bullet will just punch a .270 diameter hole. Theres probably not enough energy to make it frag. I believe Gary Roberts has stated certain 6.8 bullets will fragment reliably down to 2100 fps. My question: The photo shows the 6.8 loaded longer than the 5.56. Does that mean it's too long for mag length? John | 6.5 Grendel: The State-of-the-Art Combat Cartridge. | www.65grendel.com

It looks like the 6.8 is about .06 to .08 longer than the .223.How far out can you load a.223?

Quoted: I'm suprised it would need different mags. Both the 6.5mpc and 7.62x40 (223 case with 30 pill) utilize the standard 223 magazines, don't they? Why would this cartridge be different?

The following excerpt from Mr. Kramer's discussion in the Link I provided explains the reason for the mag mods and also answers the question of whether these rounds are over mag length (they aren't).  For the full story, read the link I provided.

I used 20 and 30 round magazines for my testing; I quickly discovered that after loading either magazine halfway I met increased resistance, mainly because the neck of my round was larger than the 22 caliber bullet used in the 223 Remington. The forward stiffing groove in the magazine that makes contact with the neck of the cartridge was forcing my cartridge with the larger neck in towards the center of the magazine, basically forcing the rounds into each other at the front. After loading 15 or 16 rounds into a 30 round magazine it started binding up any additional rounds being loaded, the magazine could be loaded with 28 rounds and fired, once the first round was chambered the magazines would most often function ok. With a 30 round magazine loaded with 28 rounds the first round would not chamber on the release of the bolt, but would go halfway into the chamber and stop going up at an angle, pulling the charging handle back a second time will fully chamber the round, after the first round was chambered the others would feed normally during firing, even on full auto testing.

Several attempts at modifying the existing 30 round magazine to accept my new round failed and it was obvious the magazine would need to be redesigned to be reliable with this new round. So the second patent was filed for a newly designed magazine. I later discovered a good magazine on the market that I could modify easily. All of the magazines I had tried so far were metal, aluminum magazines, I now had a 30 round P-Mag made by MagPul Industries, with which I had no previous experience. I first tried them in my 223 rifles and liked them, removing the floor plate revealed a small plastic ridge toward the front where the forward stiffing groove is on the metal magazines, being plastic it was much easier to modify than the metal magazines.

Much to my delight, by removing approximately half of the height of the plastic ridge from inside the magazine the magazine held a full load of my new cartridge and functioned flawlessly. Another idea I had thought about but was not sure would work until I had a magazine modified to function correctly with my cartridge is, would my modified magazine also feed .223 ammunition without a malfunction? The modified P-Mag worked fine with both the 6.8 X 45 Kramer cartridge and standard .223 Remington ammunition, which I believe is another plus for this new cartridge, the "6.8 X 45 Kramer", as magazines designed for it will also function using 223 ammunition.

height=8

Quoted: height=8 Quoted: I'm suprised it would need different mags. Both the 6.5mpc and 7.62x40 (223 case with 30 pill) utilize the standard 223 magazines, don't they? Why would this cartridge be different? The following excerpt from Mr. Kramer's discussion in the Link I provided explains the reason for the mag mods and also answers the question of whether these rounds are over mag length (they aren't).  For the full story, read the link I provided. I used 20 and 30 round magazines for my testing; I quickly discovered that after loading either magazine halfway I met increased resistance, mainly because the neck of my round was larger than the 22 caliber bullet used in the 223 Remington. The forward stiffing groove in the magazine that makes contact with the neck of the cartridge was forcing my cartridge with the larger neck in towards the center of the magazine, basically forcing the rounds into each other at the front. After loading 15 or 16 rounds into a 30 round magazine it started binding up any additional rounds being loaded, the magazine could be loaded with 28 rounds and fired, once the first round was chambered the magazines would most often function ok. With a 30 round magazine loaded with 28 rounds the first round would not chamber on the release of the bolt, but would go halfway into the chamber and stop going up at an angle, pulling the charging handle back a second time will fully chamber the round, after the first round was chambered the others would feed normally during firing, even on full auto testing. Several attempts at modifying the existing 30 round magazine to accept my new round failed and it was obvious the magazine would need to be redesigned to be reliable with this new round. So the second patent was filed for a newly designed magazine. I later discovered a good magazine on the market that I could modify easily. All of the magazines I had tried so far were metal, aluminum magazines, I now had a 30 round P-Mag made by MagPul Industries, with which I had no previous experience. I first tried them in my 223 rifles and liked them, removing the floor plate revealed a small plastic ridge toward the front where the forward stiffing groove is on the metal magazines, being plastic it was much easier to modify than the metal magazines. Much to my delight, by removing approximately half of the height of the plastic ridge from inside the magazine the magazine held a full load of my new cartridge and functioned flawlessly. Another idea I had thought about but was not sure would work until I had a magazine modified to function correctly with my cartridge is, would my modified magazine also feed .223 ammunition without a malfunction? The modified P-Mag worked fine with both the 6.8 X 45 Kramer cartridge and standard .223 Remington ammunition, which I believe is another plus for this new cartridge, the "6.8 X 45 Kramer", as magazines designed for it will also function using 223 ammunition.

Yes, I read that earlier. I was just suprised this cartridge had issues (regarding mags), where the 7.62x40 and 6.5mpc appearantly do not. Weird since the all use the same cartdige, and the dia of the bullets are relatively close in comparison (one being .3mm smaller and one being .2mm bigger). Just IMHO, the 6.5mpc and 7.62x40 may be a bit more desireable because all they really need is a barrel change, where this round creates magazine issues. Of course this is all speculation on my part, as pretty much none of us here know for sure first hand how any of these rounds work in a standard 223 AR magazine. Ican't wait until more people start backing some of these ideas and we can really get a good competition going for a new AR15 cartridge.

Quoted: Quoted: Quoted: I'm suprised it would need different mags. Both the 6.5mpc and 7.62x40 (223 case with 30 pill) utilize the standard 223 magazines, don't they? Why would this cartridge be different? All of the magazines I had tried so far were metal, aluminum magazines, I now had a 30 round P-Mag made by MagPul Industries, with which I had no previous experience. I first tried them in my 223 rifles and liked them, removing the floor plate revealed a small plastic ridge toward the front where the forward stiffing groove is on the metal magazines, being plastic it was much easier to modify than the metal magazines. Much to my delight, by removing approximately half of the height of the plastic ridge from inside the magazine the magazine held a full load of my new cartridge and functioned flawlessly. Yes, I read that earlier. I was just suprised this cartridge had issues (regarding mags), where the 7.62x40 and 6.5mpc appearantly do not. Weird since the all use the same cartdige, and the dia of the bullets are relatively close in comparison (one being .3mm smaller and one being .2mm bigger). Just IMHO, the 6.5mpc and 7.62x40 may be a bit more desireable because all they really need is a barrel change, where this round creates magazine issues. Of course this is all speculation on my part, as pretty much none of us here know for sure first hand how any of these rounds work in a standard 223 AR magazine. Ican't wait until more people start backing some of these ideas and we can really get a good competition going for a new AR15 cartridge.

Concerning magazines, This is a quote from early on in the '40' thread....

".....I have used standard metal mags, modified metal mags, standard pmags, and de-ribbed pmags....they all work....as any AR shooter has done with any caliber (5.56, 7.62x39,....) there are things that you can do to give a greater sense of security with your mags (change spring tension, add the best and new followers, the latest and greatest slick coating) any mods that I or other shooters have done to their 300-221, 300 whisper, or 7.62x40 mags is for the same sense of security more so than a mechanical requirement...."

we have de-ribbed the pmags for use with the 300 whisper and the 40....although, un-modified mags work.....in just about any detachable magazine firearm there are "tweaks" you can do to improve their basic design....rifle or pistol....I have a NFA M11A1 .380 that I have had to spend several hours on the mags getting them to stack and feed the way I want....the basic design of the mags works, the "tweaked" mags usually work better....

This is cut up excerpt from a letter I wrote to MagPul concerning the use of the 300 whisper in PMAGS.....

'I have been wild-catting cartridges for about the last fifteen years for use in the AR-15 platform....One of the cartridges that I have used along with the ones that I came up with is the 300 whisper....With heavy sub-sonic loads I along with others have found if you take a standard PMAG and de-rib it to the point that only about a quarter to half of the rib thickness remains on the interior mag wall that the 300 whisper's .30 caliber bullets stack and feed perfect in the mag....This modification is a step forward in reliability for the sub-sonic 300 Whisper loads for the AR-15.....This modification is not near as easy with conventional metal mags, usually requires a milling machine and lots of time to remove the rib on each individual mag, whereas the injection molding process would only require the change to be done once....

My question is what would it take to modify a set of your tooling to make a 300 whisper / 300-221 / wild-cat specific PMAG?.....

This 300 Whisper / wild-cat improved magazine would pull new interest into the shooting community as participants could use an off the shelf mag and choose to go with cartridges that they have stayed away from in the past due to magazine issues....I feel this would give MAGPUL definite market share with the AR wild-cat shooters.....

I am very interested in making this happen to help promote the AR 300 Whisper / wild-cat community....to the point that I would be willing to place a first lot order providing it works out to be economically practical...

Your help is very much appreciated....

Warmest Regards,

Kurt Buchert

I think a factory one time modification of the pmag tooling would open their mags up to several wild-cat cartridges including this 6.8....the side benifit is that it still works with .223 and still be considered a "standard mag" .......

my .02

40

IMO, 7x46 mm makes more sense, though it'd be too long to work in an AR15.  But this is another step in the "right" direction.  

Quoted: IMO, 7x46 mm makes more sense, though it'd be too long to work in an AR15.  But this is another step in the "right" direction.

+1

Even though it doesn't make any sense from an accountant's point of view; sometimes it is best to just start over from scratch....

I was talking about this cartridge yesterday, comparing it to the 7.62x40 which is basically the .223 round necked up to seat .30 call rounds.

I just thought you could use the same mags w/o mods.  Oh well...

Quoted: Quoted: Sounds like the .270 Ingram, circa 1979 15" Barrel with Hornady 110gr HP Spitzer Using H-335, H-322, and RE-7 powder. 2,290fps to 2,450 fps Muzzle Velocity. New?  Hardly. Cartridge dimensions the same?

The .270 Ingram was based on the .223 Remington case.  It was improved, with less case taper, to make it easier to use in the old T/C Contenders, due to lower case thrust.

It held ~30.5gr of H2O.

There is very little new under the sun.

Look at the .25-.222 Copperhead from 1969, the .240 Madame, the 6mm-222, the 6x45, the .25-.223, etc., etc., etc.

These have all been done to death.

IMO:

If you want more effectiveness out of the .223/5.56 round, use better bullets.

If you want more effectiveness out of the AR-15/M-16, use a better round, like either of the 6.X rounds.

Quoted: IMO: If you want more effectiveness out of the .223/5.56 round, use better bullets. If you want more effectiveness out of the AR-15/M-16, use a better round, like either of the 6.X rounds.

My sentiments exactly!!!  It all depends on what you want your AR to do....Doesn't it???  I am planning on getting the 6.8 SPC, but I'm sure getting one in 6.5G would also be a good choice.  

If you are truly looking for 'BIG BORE' ARs, then the 458 SOCOM or the 50B are great choices.

Like I previously stated, it all depends on what you want from your AR.  This just sounds like someone is trying to only change the barrel and have a different caliber.  This might be ok, but what happens when you grab the magazine that you thought had your 6.x or whatever and it is loaded with 5.56??? !!!

Quoted: Quoted: Quoted: Sounds like the .270 Ingram, circa 1979 15" Barrel with Hornady 110gr HP Spitzer Using H-335, H-322, and RE-7 powder. 2,290fps to 2,450 fps Muzzle Velocity. New?  Hardly. Cartridge dimensions the same? The .270 Ingram was based on the .223 Remington case.  It was improved, with less case taper, to make it easier to use in the old T/C Contenders, due to lower case thrust. It held ~30.5gr of H2O. There is very little new under the sun. Look at the .25-.222 Copperhead from 1969, the .240 Madame, the 6mm-222, the 6x45, the .25-.223, etc., etc., etc. These have all been done to death. IMO: If you want more effectiveness out of the .223/5.56 round, use better bullets. If you want more effectiveness out of the AR-15/M-16, use a better round, like either of the 6.X rounds.

I think I've said the same 'exact' thing in the past.  Very eerie indeed!

Quoted: Quoted: Quoted: Sounds like the .270 Ingram, circa 1979 15" Barrel with Hornady 110gr HP Spitzer Using H-335, H-322, and RE-7 powder. 2,290fps to 2,450 fps Muzzle Velocity. New?  Hardly. Cartridge dimensions the same? The .270 Ingram was based on the .223 Remington case.  It was improved, with less case taper, to make it easier to use in the old T/C Contenders, due to lower case thrust. It held ~30.5gr of H2O. There is very little new under the sun. Look at the .25-.222 Copperhead from 1969, the .240 Madame, the 6mm-222, the 6x45, the .25-.223, etc., etc., etc. These have all been done to death.

Looks like most of 'em were done to death before I was 10.But , something has sparked my interest only recently and so I guess I must play catch up.Despite having qualified expert with the m-16 in 1990 I had only a little interest in the ar until the SPC and Grendel came along.I've been hooked on tinkering with stuff since.

Quoted: Quoted: IMO: If you want more effectiveness out of the .223/5.56 round, use better bullets. If you want more effectiveness out of the AR-15/M-16, use a better round, like either of the 6.X rounds. My sentiments exactly!!!  It all depends on what you want your AR to do....Doesn't it???  I am planning on getting the 6.8 SPC, but I'm sure getting one in 6.5G would also be a good choice.   If you are truly looking for 'BIG BORE' ARs, then the 458 SOCOM or the 50B are great choices. Like I previously stated, it all depends on what you want from your AR.  This just sounds like someone is trying to only change the barrel and have a different caliber.  This might be ok, but what happens when you grab the magazine that you thought had your 6.x or whatever and it is loaded with 5.56??? !!!

A KB! of epic proportions is what happens...and I don't want to witness or see the results of another one of those for a long time.  

Quoted: Quoted: Quoted: IMO: If you want more effectiveness out of the .223/5.56 round, use better bullets. If you want more effectiveness out of the AR-15/M-16, use a better round, like either of the 6.X rounds. My sentiments exactly!!!  It all depends on what you want your AR to do....Doesn't it???  I am planning on getting the 6.8 SPC, but I'm sure getting one in 6.5G would also be a good choice.   If you are truly looking for 'BIG BORE' ARs, then the 458 SOCOM or the 50B are great choices. Like I previously stated, it all depends on what you want from your AR.  This just sounds like someone is trying to only change the barrel and have a different caliber.  This might be ok, but what happens when you grab the magazine that you thought had your 6.x or whatever and it is loaded with 5.56??? !!! A KB! of epic proportions is what happens...and I don't want to witness or see the results of another one of those for a long time.

My guess is that you fireform a 5.56 cartridge to 6.8.  I know I can shoot 223 through my 7 TCU contender w/ no problems, but also no accuracy & with much reduced velocity.  It might jam/fail to eject, but I would be greatly surprised if it KBd.  I know I've seen several cases where 5.45x39 was fired through a 7.62x39 AK.  It went off, sounded strange, and didn't feed the next round correctly but there was no damage.

Quoted: Quoted: Quoted: Quoted: Sounds like the .270 Ingram, circa 1979 15" Barrel with Hornady 110gr HP Spitzer Using H-335, H-322, and RE-7 powder. 2,290fps to 2,450 fps Muzzle Velocity. New?  Hardly. Cartridge dimensions the same? The .270 Ingram was based on the .223 Remington case.  It was improved, with less case taper, to make it easier to use in the old T/C Contenders, due to lower case thrust. It held ~30.5gr of H2O. There is very little new under the sun. Look at the .25-.222 Copperhead from 1969, the .240 Madame, the 6mm-222, the 6x45, the .25-.223, etc., etc., etc. These have all been done to death. Looks like most of 'em were done to death before I was 10.But , something has sparked my interest only recently and so I guess I must play catch up.Despite having qualified expert with the m-16 in 1990 I had only a little interest in the ar until the SPC and Grendel came along.I've been hooked on tinkering with stuff since.

Why not play with the Winchester Super Short Magnum cases and make something fun?  I have a 243WSSM upper, and that thing is a monster (although I haven't had it long enough to go hunting anything yet).  It's sub MOA out to 200 yards, however...so long as I hold still!

Quoted: Quoted: Quoted: Quoted: IMO: If you want more effectiveness out of the .223/5.56 round, use better bullets. If you want more effectiveness out of the AR-15/M-16, use a better round, like either of the 6.X rounds. My sentiments exactly!!!  It all depends on what you want your AR to do....Doesn't it???  I am planning on getting the 6.8 SPC, but I'm sure getting one in 6.5G would also be a good choice.   If you are truly looking for 'BIG BORE' ARs, then the 458 SOCOM or the 50B are great choices. Like I previously stated, it all depends on what you want from your AR.  This just sounds like someone is trying to only change the barrel and have a different caliber.  This might be ok, but what happens when you grab the magazine that you thought had your 6.x or whatever and it is loaded with 5.56??? !!! A KB! of epic proportions is what happens...and I don't want to witness or see the results of another one of those for a long time.   My guess is that you fireform a 5.56 cartridge to 6.8.  I know I can shoot 223 through my 7 TCU contender w/ no problems, but also no accuracy & with much reduced velocity.  It might jam/fail to eject, but I would be greatly surprised if it KBd.  I know I've seen several cases where 5.45x39 was fired through a 7.62x39 AK.  It went off, sounded strange, and didn't feed the next round correctly but there was no damage.

Definitely not what happened to the one I witnessed and the particular one I'm referring to.  Tthese were an ABolt and a BAR...and the results were scary.

Quoted: Quoted: Quoted: Quoted: Quoted: Sounds like the .270 Ingram, circa 1979 15" Barrel with Hornady 110gr HP Spitzer Using H-335, H-322, and RE-7 powder. 2,290fps to 2,450 fps Muzzle Velocity. New?  Hardly. Cartridge dimensions the same? The .270 Ingram was based on the .223 Remington case.  It was improved, with less case taper, to make it easier to use in the old T/C Contenders, due to lower case thrust. It held ~30.5gr of H2O. There is very little new under the sun. Look at the .25-.222 Copperhead from 1969, the .240 Madame, the 6mm-222, the 6x45, the .25-.223, etc., etc., etc. These have all been done to death. Looks like most of 'em were done to death before I was 10.But , something has sparked my interest only recently and so I guess I must play catch up.Despite having qualified expert with the m-16 in 1990 I had only a little interest in the ar until the SPC and Grendel came along.I've been hooked on tinkering with stuff since. Why not play with the Winchester Super Short Magnum cases and make something fun?  I have a 243WSSM upper, and that thing is a monster (although I haven't had it long enough to go hunting anything yet).  It's sub MOA out to 200 yards, however...so long as I hold still!

That does sound like fun . But right now for me , being able to use all off the shelf parts that work well and cheap brass contributes to the fun by allowing me to have more for my money.This 6.8 thing is like an American m43 (only much better in my mind), which suits me since I generally shoot no further than 100 yds.

Quoted: For military applications, the devil is in the details. He got the velocity up to 2500fps, so that sounds like he's pushing the envelope. The case size just doesn't give you much to work with. A muzzle velocity of 2600fps is specified for 6.8SPC for optimal performance out to 300 yards. If you're already pushing to make 2500, you're really not bringing much to the table. So then I noticed that it's called a "Urban Combat Cartridge". Why in the world would the US military adopt a caliber that is only useful in a limited application, when the 6.8SPC can do both? Finally, how reliable is this combination? We're not talking about a few wildcatters shooting this stuff, but your average infantryman in nasty environments. The 6.8SPC is a proven platform. Not saying this couldn't be, but it still needs to be tested. Finally - I think the need for a better caliber for the US military is obvious. The more crap like this that comes along and muddies the waters, the longer it'll be before our soldiers get a more effective weapon in their hands.

For the military app I would agree.But you can't blaim a guy for trying.And, you have to admit , it is cute.

I made up some dummy rounds using the Hornady 115 grain BTHP / WC #2715 bullet. It appears the case will shrink in length 1.740" and when seating the bullet for a C.O.A.L. of 2.260" the cannelure is no longer visible. So the case length looks to be around 1.700 to 1.710".  Remember this is all based off of a C.O.A.L. of 2.260".

It looks to me that this cartridge was made around this bullet, and if you want to go with something with more weight it will eat up the case volume pretty fast and velocity will suffer for it. All in all not to bad of a wildcat based on the .223, but I think it is somewhat limited by its bullet selection that will work.

height=8

Quoted: For military applications, the devil is in the details. He got the velocity up to 2500fps, so that sounds like he's pushing the envelope. The case size just doesn't give you much to work with. A muzzle velocity of 2600fps is specified for 6.8SPC for optimal performance out to 300 yards. If you're already pushing to make 2500, you're really not bringing much to the table. So then I noticed that it's called a "Urban Combat Cartridge". Why in the world would the US military adopt a caliber that is only useful in a limited application, when the 6.8SPC can do both? Finally, how reliable is this combination? We're not talking about a few wildcatters shooting this stuff, but your average infantryman in nasty environments. The 6.8SPC is a proven platform. Not saying this couldn't be, but it still needs to be tested. Finally - I think the need for a better caliber for the US military is obvious. The more crap like this that comes along and muddies the waters, the longer it'll be before our soldiers get a more effective weapon in their hands.

Looks like it'll be a tad slower, but still well within the frag velocities of the 6.8...
height=8

The 6.8 X 45 Kramer UCC shoots the same 115 grain bullet as the 6.8mm SPC cartridge, the SPC gets a velocity of around 2550 fps from a 16” carbine. Currently the best velocity of the 6.8 X 45 UCC cartridge is 2500 fps from a 16” carbine. The components are still being refined and we expect to get between 2550-2600 fps when production ammunition is released.

From...
http://www.defensereview.com/modules.php?name=News&file=article&sid=1143

The 6.5mpc and 7.62x40 are two I'm interested in, but I'm really not seeing much of an advantage in the Kramer over the SPC. If it required NO magazine mods, and only a barrel, it would be more appealing. The SPC seems to perform a bit better on paper, with it's only downfall to the Kramer being the fact that it'll need a different bolt where the Kramer will not.

I agree too many cartridges may muck up the military's testing, but I also believe they need to see ALL the options and get it right. The one or two that are being pushed at them right now MAY not be the best, and the best may still be to come. And even if they did adopt a cartridge RIGHT now (today), could you imagine the logistics issues and money spent trying to get every M4 or M16 in the Middle east (not to mentione the rest of the US bases around the world) updated?! I think they can take their time, keep working with the Brown Tip, M855 and Mk262 to fill the gap until the right cartridge is developed, and hopefully supply it to the troops when they're home rather than trying to add that to the mission they already have. The other option would be to screw all this small gun stuff and give them some freakin AR10's chambered in 7.62 NATO.

Quoted: I made up some dummy rounds using the Hornady 115 grain BTHP / WC #2715 bullet. It appears the case will shrink in length 1.740" and when seating the bullet for a C.O.A.L. of 2.260" the cannelure is no longer visible. So the case length looks to be around 1.700 to 1.710".  Remember this is all based off of a C.O.A.L. of 2.260". It looks to me that this cartridge was made around this bullet, and if you want to go with something with more weight it will eat up the case volume pretty fast and velocity will suffer for it. All in all not to bad of a wildcat based on the .223, but I think it is somewhat limited by its bullet selection that will work.

Essentially the same stuff that works in the SPC, 90-115gr .What you have is a more efficient M43 with 50% better range and 20-30% more energy with less wasted space and American components.I, don't believe it is enough for military app's unless we intend to maintain the 2 caliber system in place for more than 1/2 a cenrury(and switch the 308's to 260 rem!).But for anybody familiar with 7.62x39 for hunting and plinking it would be well worth the switch.

The C130 and KC135 (which get used everyday, and are also depended on), are right there in age...
he
I'm not thinking the 6.8spc can't do anything. If that's the cartridge that fits the DODs bill the best, so be it. I'd be happy to have my M4 chambered in it. The cartridges I did mention however do have some advanages over the 6.8spc, and of course the spc has it's advantages. But the idea of using say the MPC where an armorer would ONLY have to change a barrel is kind of appealing, versus having to change bolts, mags, barrels, stripper clips, and lose 5 rounds in your mag. Again, in no way am I dogging the 6.8spc and hope that the DOD keeps looking at it. But I also believe there are others that deserve a look and don't believe they are mucking anything up.

The 5.56 and early M16 is what happens when we DON't reset the counter. We've spent over 40 years trying to fix something that we just "hurried up and purchased". I do however agree that's it doesn't need to continue to drag on. In all reality, it looks as though they've really narrowed it down to some upgrades of the 5.56, the 6.8spc, and some units getting an AR10 variant. I actually wonder if a short attention span got the best of them and nothing's going to happen...

So, if Kramer is pushing this at the military who will not bite because of the bean counters I should go ahead with my 6.8x43/17 rem? The article did say lawyers and patents for this and that.Probably wouldn't hit the market as soon as I'd like.

I'll call mine the M43 American or AM43.

-Is this the procedure:

                                -reamer=17 rem + neck changes ($)
                                 
                                -send reamer to die maker($)

                                -send reamer to gunsmith +$$$(17rem head space)

*I implore the military to not look into this cartridge as it is my own foolish endeavor.

The best it can do completely maxed out now is 2500?  
At this point with the 6.8 they were getting 2750 max'd.
They say they will get more as they refine the cartidge?
I'll believe when I see it!!! I don't think I beleive the 2500 is really possible with ammo that has to meet the variations seen in comabt.
There is only so much that can be had with that little amount of powder. If I am adding it up right 22 grain H2O usable capacity with the 115 SMK in the Kramer case seated to 2.26 OAL gotten from Quick Load

The SPC is a very efficient cartridges.  The 30 BR is the only one that comes to mind right now that is slightly better. If they are saying they are getting 2500 with 8 grains less powder Hmmm.  If so it is max'd or over as I don't really think they would put forth a conservative number do you!?!  Are those loaded to 2.26 or longer?

Look at what we are always told about a round when its still in developments. The big marketing push of how this round will do this or that. It always comes out a bit short.

If this is getting 2500 now compared to the SPC 2750 when it was in testing then I think we can expect when you put the durability and temperature variations it has to deal with it will be lower not higher. We lost 100-125 from the SPC to have it handle the combat environment. 100 FPS off the Kramer gives you a 2400 from a 16" .

What about its performance from a SBR barrel?

What are the numbers from a 10.5", 11.5", 12.5" barrels? What the SPC was designed to be use in specifically.

When the group that created the SPC was looking for the round do we honestly think that they didn't look at just necking up a 5.56 case?

I wonder why they didn't do something so simple? Maybe cause it didn't fill the requirement that were needed.

Lets look at this:

SPC Case Usable Powder Capacity : 30.5 H2O 115 SMK with OAL 2.26"

Kramer Case Usable Powder Capacity : 22.5 H20 115 SMK with OAL 2.26"

The Kramer has 8 grain less capacity.

SPC Case body diameter .403

Kramer Case body Diameter: .355

Fatter cases tend to burn the powder column more efficiently then narrow powder column.

Bore is the same so the only thing effecting velocity is the efficiency of the burn and the amount of powder.

With the SPC we are getting about 85-89 FPS per grain of powder for the 115. That is very high Ballistic Efficiency of about 32% with a 2650 fps of 115 SMK from a 16"

The 30 BR considered the bench mark for the best Ballistic Efficiency is at 33% best case with its loads.

They are claiming they will with tuning and tweaking get 118 fps per grain of powder with a 115 gr bullet to get 2600 from a 16" which would give it a Ballistic Efficiency rating that would crush even that of the 30 BR by a huge margin!?!  That would be 31 FPS more per grain of powder capacity then the SPC or 33% more power from each grain of powder.  I would love to get some of the powder that does that with the pressure ratings of the AR and its bolt.  To show how crazy that is if I could get that from my SPC then I could drive the 115 SMK to 3540 FPS on 30 gr of powder and that would have to be with pressure not over 60K hell even 100K PSI and thats from a 16" barrel!!  Even 2500 seems out there as that is a still over 110 fps per grain of powder capacity.

I could be wrong but I think some claims are being stretch considerably to try and get it close enough to the SPC to get some attention and make the idea of not having to change a bolt to make it look appealing. I have to admit the idea of using the same case and one less part to swap in appealing but not at the cost of a very sizable reduction in performance over the present SPC. Thinks its hard to make the case for the extra lethality with the full bore SPC try watering it down by 200 + fps and decrease the real world difference from that and the 77 gr 5.56.


Like was previously said all this type stuff does is add confusion and muddy things up to getting a better round by attaching to the coat tails of the 6.8 SPC s success that is continuing to grow considerably.

Nice Tim_W. I was going to ask the same questions. I appreciate anyone's ingenuity, but I did notice the 2500 fps quoted for the Kramer and I was going to ask questions about the case capacity in relation to the 6.8, along with the efficiency of both cartridges.

At 2500 fps or less, and being quoted as an "urban combat cartridge", this may be a great idea for some applications. But as soon as the military adopts an urban cartridge we'd end up in a long range shooting war across the desert with the Iranians.

This round appears to be a distraction to the current testing and evaluation. I'm open to more information, but right now I agree with Tim and Zhukov.

I can see the positions of the 6.5 and 6.8 rounds in an open discussion, but this Kramer cartridge is not in the same category.

270 TCU Contender.

Quoted: Quoted: Quoted: Quoted: Sounds like the .270 Ingram, circa 1979 15" Barrel with Hornady 110gr HP Spitzer Using H-335, H-322, and RE-7 powder. 2,290fps to 2,450 fps Muzzle Velocity. New?  Hardly. Cartridge dimensions the same? The .270 Ingram was based on the .223 Remington case.  It was improved, with less case taper, to make it easier to use in the old T/C Contenders, due to lower case thrust. It held ~30.5gr of H2O. There is very little new under the sun. Look at the .25-.222 Copperhead from 1969, the .240 Madame, the 6mm-222, the 6x45, the .25-.223, etc., etc., etc. These have all been done to death. Looks like most of 'em were done to death before I was 10.But , something has sparked my interest only recently and so I guess I must play catch up.Despite having qualified expert with the m-16 in 1990 I had only a little interest in the ar until the SPC and Grendel came along.I've been hooked on tinkering with stuff since.

The .270 Ingram, and the 6.5/7 TCU rounds were designed to knock down 55lb steel rams in IHMSA w/o alot of recoil in XP-100 and Contender pistols.

I do not think that the 6.8x45 UCC, or the 6.5 MPC, will be that much better than the improved 5.56 rounds to warrant the changeover.

The 6x45 (.223 Rem necked up to 6mm) is a great little round...as long as you keep bullet weight under 90grs, 85gr better, due to limited case capacity.

So the question is, just how much better is the 6x45 than the 5.56x45, when comparing bullets with similar SD's.

The answer has been....not enough to warrant the complete change over for US Armed Forces.  The larger diameter bullets have an even bigger trade off, which is low velocity.

Now, if you, as an individual, wish to tinker, be my guest.  Tinkering is fine, as far it goes.

Using the right bullet, the 6x45 is a wonderful round for light game (70-150lbs) to 250 yards or so.

Either 6.X round is a better choice, given the constraints of the AR-15/M-16 magazine well.

In M-4 length barrels to 300 meters, there is little difference between the two 6.X rounds, in terms of wind drift and bullet drop.

Look at which 6.X round best serves your needs and go with it.

Quoted: Quoted: Quoted: Quoted: Quoted: Sounds like the .270 Ingram, circa 1979 15" Barrel with Hornady 110gr HP Spitzer Using H-335, H-322, and RE-7 powder. 2,290fps to 2,450 fps Muzzle Velocity. New?  Hardly. Cartridge dimensions the same? The .270 Ingram was based on the .223 Remington case.  It was improved, with less case taper, to make it easier to use in the old T/C Contenders, due to lower case thrust. It held ~30.5gr of H2O. There is very little new under the sun. Look at the .25-.222 Copperhead from 1969, the .240 Madame, the 6mm-222, the 6x45, the .25-.223, etc., etc., etc. These have all been done to death. Looks like most of 'em were done to death before I was 10.But , something has sparked my interest only recently and so I guess I must play catch up.Despite having qualified expert with the m-16 in 1990 I had only a little interest in the ar until the SPC and Grendel came along.I've been hooked on tinkering with stuff since. The .270 Ingram, and the 6.5/7 TCU rounds were designed to knock down 55lb steel rams in IHMSA w/o alot of recoil in XP-100 and Contender pistols. I do not think that the 6.8x45 UCC, or the 6.5 MPC, will be that much better than the improved 5.56 rounds to warrant the changeover. The 6x45 (.223 Rem necked up to 6mm) is a great little round...as long as you keep bullet weight under 90grs, 85gr better, due to limited case capacity. So the question is, just how much better is the 6x45 than the 5.56x45, when comparing bullets with similar SD's. The answer has been....not enough to warrant the complete change over for US Armed Forces.  The larger diameter bullets have an even bigger trade off, which is low velocity. Now, if you, as an individual, wish to tinker, be my guest.  Tinkering is fine, as far it goes. Using the right bullet, the 6x45 is a wonderful round for light game (70-150lbs) to 250 yards or so. Either 6.X round is a better choice, given the constraints of the AR-15/M-16 magazine well. In M-4 length barrels to 300 meters, there is little difference between the two 6.X rounds, in terms of wind drift and bullet drop. Look at which 6.X round best serves your needs and go with it.

Or you can just say screw it and go with an upper chambered in 243 WSSM which will push a 100 grn round over 3000 fps.  That's plenty of knockdown...

Couple of minor observations on various posts:

Mention of patents (and lawyers) - who cares.  So you filed an application.  Last patent I recall seeing approved on cartridge design was the famed Jamison patent which covered the aspects of the WSM and RSAUM (Jamison did the work up and defined the range of dimensions that made the "sweet spot", despite numerous wildcats of similar size having come before).  

Performance of smaller cases - between two technologies that exist it is feasible to get substantive improvement in performance without exceeding peak pressure.  Both have been brought to the attention of DoD (ARDEC, etc).  At least one suffered the famed "NIH" fate ("it's too different, too radical, no matter what your strain gauges show, it can't be true")  From an engineering PoV, it is one of those "forehead slaps".  BUT, it comes with a price - as always there is a trade off.  Using these technologies it is fully feasible to get some amazing performance.

Binding in the magazine - even JD Jones has commented that his .300 Whisper would not work with all mags and that he suggests taking something like a dowel rod and ramming it down the front of the mag to slightly push the front rib out ... 6.5 MPC shouldn't have this issue as the neck OD should be small enough.  Making the case shorter on the Kramer would possibly alleviate the issue - have the neck end just before the rib.  Seating the bullet deeper in a longer case versus not as deep in a shorter case does not make THAT much of a difference, plus is rather cumbersome to try and take advantage of what little extra powder space might exist between the base of the bullet protruding into the case and the case wall.

It makes a great competitor against the 7.62x39.From both the efficiency standpoint and component availability.

ETA- it makes an interesting comparison when you place a 7.92x33 next to a 7.62x39 and then this 6.8x43.As you progress from the 7.92 to the 6.8 the bore to body diameter ratio changes to the extent that there is probably a similiar ratio in expanding combustion chamber advantage.Not to mention the range and round count advantage and the pressure advantage of having a smaller bolt face.This cartridge shows that it can make the 5.56 outperform the 7.62x39 in it's intended performance envelope but it is a shadow to the 6.8 spc in overall mission which is one advantage the 5.56 always had over the 7.62 and that is range.If they maintained the two tier system this would be a great little cartridge but then again they should institute the 6.8 spc and reap the benefits of a one tier system, maybe keep a couple of m-14's around rechambered in 260 rem for fun.

I see the 6.5 MPC (and likely the 6.5 Kramer UCC) dogged by the same issues that dog the 6.5 Grendel; that being a strictly held patent on the cartridge thereby strangling any further development of the design.  On paper, the Grendel has the potential to best the SPC, MPC, and UCC, however, it ain't ever going to happen because of the tight patent control Alexander Arms exercises over the Grendel.

This "6.8x45 Kramer Urban Combat Cartridge" is a cool idea.  Thanks for the
article link.  I'm glad they gave us a lot of the "behind the scenes"
development work.  Yeah, the name is too long and is perhaps trying to
attact those who are sold/attracted to all things named "combat" - "6.8x45
Kramer" would be fine by me.

I wouldn't be mis-led into thinking the comparison picture shows the 6.8
Kramer being loaded longer than magazine length or longer than the 5.56
shown next to it - perhaps the 5.56 was loaded shorter than maximum mag
length.  Besides, the article indicated he was using fully loaded mags, so
he can't be loading over magazine length in those instances.

The full-case water volume of 6.8 Kramer should be around 31.5gr (which is
the spec for my 7mm TCU cases).  For 6.8 SPC the water volume is 34.6gr.  
The difference is 9.8% greater to the SPC case.  So, we should expect Kramer
velocties to be around .098% less than SPC for a 115gr:  2,345 fps vs 2,600
fps in a 16" barrel.

It was "out of the box" thinking for him to pull 6.8 SPC loaded rounds for
the powder inside to work-up his loads to 2,500 fps.  It shows he wanted to
get the maximum performance velocity possible from the 5.56 case - an "A"
for effort I say.  I'd like to see his velocity differences between Hornady,
Remington, and SSA powders, along with off the shelf powders.  The 2,500 fps
number for a 115gr out of a * 16" * seems a bit high, whereas 2,350 would be
more believable.

It's all about trade-offs and choices, and this cartridge adds more of both
to the AR15 platform.  Again, cool.

I'd love it if P-mags were made without the internal front guide rib for all
us wildcatters, +11-teen on that.

Quoted: The full-case water volume of 6.8 Kramer should be around 31.5gr (which is the spec for my 7mm TCU cases).  For 6.8 SPC the water volume is 34.6gr.   The difference is 9.8% greater to the SPC case.  So, we should expect Kramer velocties to be around .098% less than SPC for a 115gr:  2,345 fps vs 2,600 fps in a 16" barrel.

Nice post Chris, this is what I'm curious about.That roughly 10% case capacity advantage of the SPC and your velocity figures are certainly in line.But if we compared two cartridges of a more extreme example such as the 300 whisper and the 7.62x39 we see an efficiency advantage in the whisper.I would like to know what percentage of case capacity the 7.62x39 has over the whisper and if this can be extrapolated inversely to the UCC vs SPC?I think the case capacity limitation issue is well established but I would like to see just how much ground can the UCC make up between 2345 and 2600 using a possible efficiency advantage.We know folks selling things have a tendency to hype but I would like to know how much is real.

ETA-looks like 25gr vs 35gr in the whisper/m43 comparison , so about a 33% capacity advantage to the m43.And the whisper comes within 100-150 fps of the m43.Now the whisper has a higher bore to capacity ratio than the UCC but is that enough to diminish the advantage needed for the UCC to bridge the 10% gap between it and the SPC?(I do understand also that the SPC operates at a higher pressure than the m43)

ETA-given the SPC and UCC have the constant of same bore diameter and bullet weight with the exception of 10% case capacity the UCC could run 10% faster burning powder since in a same length of bbl it would essentialy have a faster dissapative nature in regard to the pressure.I believe this cartridge is very capable of making 2600fps.I would take my time getting there and use the lightest bullets first though.

Quoted: ... Nice post Chris, this is what I'm curious about.That roughly 10% case capacity advantage of the SPC and your velocity figures are certainly in line.But if we compared two cartridges of a more extreme example such as the 300 whisper and the 7.62x39 we see an efficiency advantage in the whisper.I would like to know what percentage of case capacity the 7.62x39 has over the whisper and if this can be extrapolated inversely to the UCC vs SPC?I think the case capacity limitation issue is well established but I would like to see just how much ground can the UCC make up between 2345 and 2600 using a possible efficiency advantage.We know folks selling things have a tendency to hype but I would like to know how much is real. ETA-looks like 25gr vs 35gr in the whisper/m43 comparison , so about a 33% capacity advantage to the m43.And the whisper comes within 100-150 fps of the m43.Now the whisper has a higher bore to capacity ratio than the UCC but is that enough to diminish the advantage needed for the UCC to bridge the 10% gap between it and the SPC?(I do understand also that the SPC operates at a higher pressure than the m43)

I just measured a 7.62x39 full case water volume at 33.8gr. or 0.8gr less than 6.8SPC.  

Is that 300 Whisper 25.0gr of water filled to top of neck?

It's hard enough two compare 2 cartridges like 6.8 Kramer to 6.8 SPC, but throwing in 300 Whisper and 7.62x39 and extrapolating back is makings for a good spaghetti.

It's probably best to shoot all comers side by side on the same day, detail the specs and results, and pick the one that meets most of your requirements.

I'd love to read about a boar/deer hunt with this 6.8 Kramer someday.

Edit:  corrected 7.62x39 water measurement from balance beam, after getting my digital scale warmed up and rezeroed.

I look at the 6.8 SPC as a 7.62x39 that the American formula(5.56) was applied to with higher operating pressure and smaller diameter bullet.(given same boiler room size).So if you can boost a whisper to perform supersonically similar to the m43 the Kramer  could be the enhanced whisper version of the SPC.I just think it is interesting to try to pin down the attributes that make it perform the way it does or could instead of reject it out of hand because supposedly it has been done before or doesn't meet your performance standard.

Disclaimer-this is not an endorsement of this cartridge for the DoD

ETA-also note that a 115gr SPC@2600FPS drops to 2500fps @ 30 yards.