This may not be new to all, but I heard that some of the High Power AR shooter's are necking down the 6.8 SPC to a 6mm bullet with some pretty successful showing - Anyone know more on this topic?

various places OAA... you can find 6mm, .257, 6.5 and a .30

The rabid wildcatters work fast

Quoted: various places OAA... you can find 6mm, .257, 6.5 and a .30 The rabid wildcatters work fast

God luv'em.

Quoted: Quoted: This may not be new to all, but I heard that some of the High Power AR shooter's are necking down the 6.8 SPC to a 6mm bullet with some pretty successful showing - Anyone know more on this topic? John Holliger started it a while ago, and already has the chamber reamer made.  You can contact him at www.whiteoakprecision.com

No kidding.....I was just on the phone with John the other day ordering one of his service rifle uppers.  John asked me about another co-shooter (who, by the way told me about the 6mm SPC) in my area who wanted 6mm SPC upper and he was having a hard time getting a hold of him to get the spec's on the upper to build for him. So John Holliger is the source of this - Heck,  if I would have known this I could have gotten quite a education on the 6mm SPC. I don't think I'll call him now, as he was pretty busy, but next time I'll get the full scoop on the 6mm SPC performance.

heavier 6mm/.243 have some of the best BC ratings out there. seems an obvious choice for the wildcaters.

It shouldn't be terribly surprising since folks have been necking up the .219 Donaldson Wasp case for decades.  The Wasp's case is nearly the same size and shape (except for caliber and rim) as the 6.8mm SPC.  Marty ter Weeme has actually played with necking the 6.8mm SPC case down for .224" projectiles using dies for the .219 Wasp.

I wonder how the 6mm SPC compares to cartridges such as the 6mm PPC or 6x45mm (6mm/223). From what I have read the 6mm PPC when used in the AR15 platform can not reach the same pressures levels of a bolt action rifle without stressing the bolt and this can result in premature bolt failure. By lowering the pressure for the 6mm PPC it takes away any advantage it had over the 6x45mm, and puts them about equal for bullets up to around 90 grains.

So I am asking what if any real advantage does the 6mm SPC offer over other existing 6mm cartridges chambered in the AR15.

Joe

Quoted: I wonder how the 6mm SPC compares to cartridges such as the 6mm PPC or 6x45mm (6mm/223). From what I have read the 6mm PPC when used in the AR15 platform can not reach the same pressures levels of a bolt action rifle without stressing the bolt and this can result in premature bolt failure. By lowering the pressure for the 6mm PPC it takes away any advantage it had over the 6x45mm, and puts them about equal for bullets up to around 90 grains. So I am asking what if any real advantage does the 6mm SPC offer over other existing 6mm cartridges chambered in the AR15. Joe

I believe most of the bolt failures on PPC ARs are due to weakening of the lugs caused by the metal removed to open thebolt face enough to accept the PPC's base.

Quoted: So I am asking what if any real advantage does the 6mm SPC offer over other existing 6mm cartridges chambered in the AR15.

IIRC, the 6 mm SPC has a greater case capacity than the 6 mm PPC and the 6X45.

Quoted: heavier 6mm/.243 have some of the best BC ratings out there. seems an obvious choice for the wildcaters.

Bested only by the 6.5 mm.

I am sure by now you all know that several different caliber SPC variants were initially tested, including 6mm and some of the folks involved in SPC development have indeed shot different versions for Hi-Power...

SWO_daddy wrote:
I believe most of the bolt failures on PPC ARs are due to weakening of the lugs caused by the metal removed to open thebolt face enough to accept the PPC's base.

You are correct about this but their are two things that happen when you remove more metal from the bolt for cases with a larger case head diameter. One is less locking lug area for engagement and two more surface area for the case to push against the bolt face (bolt thrust). While you will see this as less of problem with the case head of the parent 6.8 SPC case head diameter of  .422"
it is still an issue to consider.

Joe

DocGKR:
Thanks for adding the pic of the different calibers. While they were tested in the development of the 6.8 SPC not much has been made available as to how well each performed as far as velocity with bullet weights for each of the calibers shown.

Joe

Quoted: various places OAA... you can find 6mm, .257, 6.5 and a .30 The rabid wildcatters work fast

Who you calling rabid?

So I used 219 Don Wasp tooling to make a 11.5" barrel in .223 WASP/C and 30 Herrett tooling to build a couple of .30 HRTs ....

BTW, got the CAS-V, schweet, got a brand new 14.5 HBAR 338 here with your name on it.  Assume 14.5 is OK?

I wonder if you could neck down 6.8SPC enough to have a 5.56SPC using the heavy 80-90gr .224 bullets.

Quoted: DocGKR: Thanks for adding the pic of the different calibers. While they were tested in the development of the 6.8 SPC not much has been made available as to how well each performed as far as velocity with bullet weights for each of the calibers shown. Joe

I would like to see some specs on the 6mm-SPC, my SWAG was that it would make a nice varmint round.

Quoted: I wonder if you could neck down 6.8SPC enough to have a 5.56SPC using the heavy 80-90gr .224 bullets.

Yes, this is what the 223 WASP/C (AKA 219 Donaldson Wasp Rimless) was for.  Using 55000 psi, a 16" barrel and 80 gr SMK, it comes in around 2650 fps.  You can clean up an existing non-chrome chamber with the 219 DW reamer and use a 6.8 bolt for head space check.  Forming the brass was a bear and lost several, but suspect this was due to the fact that the brass appeared to be some of the earliest stuff made and abused at that (range pickup from .mil T&E)

I have a picture of the last remaining loaded round with a 77 SMK Moly somewhere, may even still have the round ...

Quoted: Quoted: DocGKR: Thanks for adding the pic of the different calibers. While they were tested in the development of the 6.8 SPC not much has been made available as to how well each performed as far as velocity with bullet weights for each of the calibers shown. Joe I would like to see some specs on the 6mm-SPC, my SWAG was that it would make a nice varmint round.

I would like to see some good data on this cartridge also. I am not knocking the 6x43mm or 6mm SPC, and if it has some clear cut advantage over my rifles chambered in 6x45mm will consider it for a future build.

Joe

Quoted: I wonder if you could neck down 6.8SPC enough to have a 5.56SPC using the heavy 80-90gr .224 bullets.

One company has worked on it, and it may be something that gets built/released to the public in a year or so.

Quoted: ...with the case head of the parent 6.8 SPC case head diameter of  .422". Joe

The case head on the PPC is .440", so yep, slightly larger.  

One additional issue to consider when thinking about necking down and using heavier longer bullets in a 6x43 SPC is that you have to have the bullet seated so deep into the case body that accuracy can be compromised.  You are really eating up powder capacity as well.  That is if you stay with mag length rounds.  

Imagine shooting a Sierra 80 at mag length and how much of the bullet is down into the case.  

Optimal accuracy is obtained with the bearing surface of the bullet protruding into the case no further than the neck shoulder junction.  The boat tail can extend past, but once the body of the bullet starts past this area, nothing positive happens to accuracy.

Seated long however, a 6x43 with a Sierra 107, should work real well.  

Also, there are many 6mm bullets that you could try, including flat base Benchrest bullets that would not have the problems I mentioned above.   For example, a Berger 88 High BC flat base, a flat base VLD bullet.  This bullet currently owns the IBS 600 yard World Record group, .8 inches for 5 shots at 600 yards.   This was shot out of a 6BR bolt gun, but, could be pretty nasty as a target bullet out of a 6x43.    Just something to think about....    

 

Quoted: I wonder if you could neck down 6.8SPC enough to have a 5.56SPC using the heavy 80-90gr .224 bullets.

Basically it's been done.  If you happen to have a copy of Zediker's The Competitive AR-15 there's a pic of a .224 caliber wildcat based on the .30 Remington case, which happens to also be the parent case of the 6.8 Rem SPC.  The real question is how it would perform as a target cartridge and given that maximum velocity often doesn't equate to optimal accuracy, so what would be the point?

I'm waiting to see how John's 6mm-6.8SPC project works out.  The initial numbers that he mentioned at Perry were around 2800 fps with the 107gr SMK, however, a post a couple months ago on another HP board stated that a tester was getting 2650-2725 fps.  That really didn't surprise me since the guys in the 6.8 thread on the AR board are having a tough time pushing 110-115 gr .277 bullets much past 2600fps in the 18-20" barrels.

I'm no expert, but it seems to me that the added case capacity of the 6.8 cartridge is easily eclipsed by the added weight of the projectiles over .223 options such as the 90gr JLK.  If the 6.8 can't be pushed past 2700fps, then a similar weight 6mm bullet with a longer bearing surface isn't going to get there either.  If you really want to live on the wild side then I have a feeling the top dog cartridge for the AR platform would be a 6mm BRX, but who really wants to turn rims?  And then there's the issue of getting it to feed reliably which probably means making your own single stack mags...

WalkerTexasRanger:

I took a look at some of the longer bullets I have for the 6mm and compared a 6.8 spc case to get an idea of overall length. With the case for the 6.8 spc being shorter than the .223 by 2mm it helps with seating the longer bullets. The ones I had on hand were Nosler 95 gr BT. Hornady 100 gr BTHP, and 95 gr SST.

In general the PRI mags allow one to seat bullets out a little farther to around 2.285", if the chamber will permit. So at this point I can see the added bullet  weight to be a plus for the 6x43mm, But at the same time would like to see some solid load data with velocities for bullets 90 to 107 grain range.

GcS:
Thanks  for the info, I think the wildcat you refer to was the .240 Madame. John built both of my 6X45mm barrels and after working with this cartridge in the AR believe 90 gr. bullets are about as heavy as you want to go. I was able to get a 85 grain bullet to 2700 FPS out of the 20" barrel.

I can see that the 6X43mm may be the best option if you want to shoot 6mm bullets above 90 grains.

Joe

The idea that most appeals to me for a magazine-length 6mm in the AR platform is from military writer Stan Crist: Neck the .223 case to 6mm and shorten it, giving a 6 x 41 loaded with something like a 90gr Lapua Scenar.

John

Quoted: The idea that most appeals to me for a magazine-length 6mm in the AR platform is from military writer Stan Crist: Neck the .223 case to 6mm and shorten it, giving a 6 x 41 loaded with something like a 90gr Lapua Scenar. John

So this would be close to the 6mm/222 with the case neck shortened to get the case length to 41mm. This would give you around 25 grains of powder capacity and probably about 2400 FPS max with the 90 gr. Scenar out of a 20" barrel.

Joe

Quoted: GcS: Thanks  for the info, I think the wildcat you refer to was the .240 Madame.

IIRC, it is referred to as the 22 Bartlett-Wylde-Rat in Zediker's book.

Quoted: Quoted: GcS: Thanks  for the info, I think the wildcat you refer to was the .240 Madame. IIRC, it is referred to as the 22 Bartlett-Wylde-Rat in Zediker's book.

I need to read things a little slower and let them sink in some, missed the fact that GcS was talking about a .22 caliber wildcat. The .240 Madame is a 6mm wildcat on the  .30 Remington case.

Joe

Quoted: Quoted: I wonder if you could neck down 6.8SPC enough to have a 5.56SPC using the heavy 80-90gr .224 bullets. Basically it's been done.  If you happen to have a copy of Zediker's The Competitive AR-15 there's a pic of a .224 caliber wildcat based on the .30 Remington case, which happens to also be the parent case of the 6.8 Rem SPC.  The real question is how it would perform as a target cartridge and given that maximum velocity often doesn't equate to optimal accuracy, so what would be the point?

As Marty and I said before, this would essentially be a rimless .219 Donaldson Wasp.  The Wasp was a very popular Benchrest competition cartridge until the .222 Remington displaced it.

Using published information, you can generate a rough/general time line

30-30 Winchester - designed and marketed in 1895 for the 1894 lever action

30 Remington - introduced 1906 for the Model 8 autoloader.  More or less the rimless version of the .30-30 and first called the .30-30 Remington ... now considered obsolete

219 Zipper - 1937 by Winchester, a 22 cal version of the 30-30

219 Donaldson Wasp - 1937, shortly after the 219 Zipper was introduced.  More or less a shorter, improved Zipper

6mm/30-30 - wildcat first documented in the mid 1940s

225 Winchester - similar to the 22/30-30, shortened and smaller rim.  1964 vintage

30 Herrett - 30-30 shortened and improved, 1972

270 JDJ - 6.8 version of the 225 Winchester case, improved, could be seen as the original precursor to the 6.8 SPC (a rimmed version).  Don't tell JD I said that, though! 1978

30 American - special version of 30-30 brass with small primer and small flash hole for match grade versions of the 30-30 wildcats.  1986

There are others such as the 7 x 40 based on the .30 Remington that were used in competition.  

So there is not really much new under the sun.  While indeed one could go out and "develop", "design" or "invent" a new version of a wildcat based on the 6.8 case, we felt that it would be easier, faster, cheaper to use existing tooling.  If a customer can take an existing .223 barrel, clean up the chamber with a 219 DW reamer and use existing 219 DW dies, to us, that seems to make sense.  You can load the heavier bullets without having to seat them too deep, you get better performance than the .223, load data is available for starting loads ....

By no means am I marginalizing the work of the SPC team, Docs pics show they have been there, done that, gone over all the old versions.  Just seems some of the writers out there have forgotten their history (just like one who said there was nothing in the US arsenal remotely similar to the FN 5.7 x 28.  Seems the Hornet and 5.7 MMJ slipped his mind ...)

From my little corner of the world, it would seem that the 22 version would have made sense, as it would allow use of the existing projectiles, barrel blanks, flash hiders, suppressors, etc.  Bolts and magazines are all that needed to be changed.  223 would not chamber in the 22 SPC and the other way around.  The 22 SPC in a 10.5" should outperform the M855 and improve the effective distance (I was unable to duplicate the M855 velocities in the Ammo Oracle FAQ without going to very high pressure but this is likely a limitation of my software and not a reflection on the validity of the data)

Anyway, I dug up the 10.5" 22 SPC barrel and if someone is interested, I can see about firing some rounds of a chrony and seeing what it might do ....