Too little - too late. He appears to have just copied the 6 mm x 45 which has been around along time as a wildcat. It has never been very popular as case just doesn't hold enough powder for improved performance. It would make more sense to neck down the 6.8 to a 6 mm or else we have the Grendel to go to for a bit more performance.

Thats it,call the time...

shoulder on the 6.8 reminds me of .300 savage, hmmm that would be a badass AR round 6.8 savage

Quoted: shoulder on the 6.8 reminds me of .300 savage, hmmm that would be a badass AR round 6.8 savage

Uhwarrie, you ever shoot at Flintlock Valley?

Anybody with experiance with the 300 whisper , would slow burning pistol powders benefit this cartridge?I am interested in doing a work up as if this were a supersonic whisper to see if any gains or if pistol powders are even viable in this cartridge.I would probably be working with a 16" bbl to get the bullet out as fast as possible if that helps.i'm looking for something roughly 10-15% faster than what the SPC is running with.I'm green!

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.

That is interesting that only the 115gr bullet is being looked at here.2580 fps shouldn't be too difficult to hit with the 110gr and 2700 fps with the 90gr.There are some great performing bullets in this narrow band for self defense to medium game and varmints.It becomes easy to see when you bring the 6x45 into the comparison since the upper range is around 80-90gr between 2700-2800fps.For the hobbyist the ability to retain bolt , mag, and brass is a force multiplier.

Quoted: 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. That is interesting that only the 115gr bullet is being looked at here.  2580 fps shouldn't be too difficult to hit with the 110gr and 2700 fps with the 90gr.  There are some great performing bullets in this narrow band for self defense to medium game and varmints.  It becomes easy to see when you bring the 6x45 into the comparison since the upper range is around 80-90gr between 2700-2800fps.  For the hobbyist the ability to retain bolt , mag, and brass is a force multiplier.

I'm looking at my Sierra 5th Edition reloading manual, page 284 for the 6x45mm, which shows an 85-90gr bullet maxing at 2,700fps from a 24" Winchester M70 ...so, coming back down to Earth now, a 16" AR should be in the neighborhood of 2,425fps for a 90gr. bullet.  Which should make one re-question that claimed 16" 2,500fps for a heavier 115gr bullet.

I too like the advantages the 6.8 Kramer offers, just need a little video proving mag-fed 115gr rounds are hitting their advertised "mark".

Quoted: 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.

OT, but there is no 'tight patent control' with AA, vis-a-vie the Grendel.

Not to change the subject but has anyone considered necking down the 6.8spc to 6mm or 5.56mm?

Quoted: Quoted: 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. That is interesting that only the 115gr bullet is being looked at here.  2580 fps shouldn't be too difficult to hit with the 110gr and 2700 fps with the 90gr.  There are some great performing bullets in this narrow band for self defense to medium game and varmints.  It becomes easy to see when you bring the 6x45 into the comparison since the upper range is around 80-90gr between 2700-2800fps.  For the hobbyist the ability to retain bolt , mag, and brass is a force multiplier. I'm looking at my Sierra 5th Edition reloading manual, page 284 for the 6x45mm, which shows an 85-90gr bullet maxing at 2,700fps from a 24" Winchester M70 ...so, coming back down to Earth now, a 16" AR should be in the neighborhood of 2,425fps for a 90gr. bullet.  Which should make one re-question that claimed 16" 2,500fps for a heavier 115gr bullet. I too like the advantages the 6.8 Kramer offers, just need a little video proving mag-fed 115gr rounds are hitting their advertised "mark".

One variable that you would have to look at when comparing a 90gr 6x45 to a 90gr 6.8 going out a 16" tube is bore diameter.After you have fired the round and just before the bullet exits the muzzle you have two very different sized combustion chambers.If the 6.8 has a 10% larger bore you have a 10% more potential for velocity(maybe, with faster powders).So, 2425 could potentialy be 2667 in the 6.8 and alittle more possibly if it can utilize the faster powder.And that is just the 16" bbl.

ETA- oops, must have been thinking of the difference between .308 and .277.There is almost 15% difference between .243 and .277.So, 2425 could be 2770 in the 6.8.Bigger pistons make bigger power.

Quoted: Not to change the subject but has anyone considered necking down the 6.8spc to 6mm or 5.56mm?

Yup, the 5.56X42 DMR and 6x41.

See AR15 Performance

Uh...we originally tested all those other caliber configurations for the original SPC trials back in 2002:

Quoted: Quoted: 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. That is interesting that only the 115gr bullet is being looked at here.2580 fps shouldn't be too difficult to hit with the 110gr and 2700 fps with the 90gr.There are some great performing bullets in this narrow band for self defense to medium game and varmints.It becomes easy to see when you bring the 6x45 into the comparison since the upper range is around 80-90gr between 2700-2800fps.For the hobbyist the ability to retain bolt , mag, and brass is a force multiplier. Note that I said "For MILITARY applications..."

Maybe a eastern european country looking to replace 7.62x39 or 5.45x39 with a nato rimsize.It would have more range and energy than the M43 and in the right platform probably more accuracy than the 5.45 and more rounds in a mag than both.Anyway there is not alot more that can be said for this cute little cartridge .Mr Kramer likely will not hit the mother load with a government contract and rightly so as this cartridge is too much of a lateral move to adopt.It might be nice, however, for someone who has not yet played with a 6x45 or 25 copperhead.

ETA-Got an e-mail reply back from Mr Kramer , should have a web-site up shortly .Will be offering 16" uppers and dies should anyone be interested.

Just a point of fact the case capacity of SSA cases which are then ones used along with ammo for current testing and performance numbers is 36.50 H20 to case mouth at minimum case 1.672 at the SAAMI trim to 1.676 it would be more although I have not measured it yet as the other is my trim to.
 
I didn't realize the Kramer had a 31.5 capacity as the largest 5.56 case I had seen listed had 30.6 H20 capacity.  Then I realized I forgot to take into account the increase in the diameter of the neck as that would give it more H20 although that would be taken up by the larger bullet.  To keep a COAL of 2.26 the bullet will have to set deeper into the case as it is longer then the SPC.  This would increase the deficient even more.  

Quoted: Just a point of fact the case capacity of SSA cases which are then ones used along with ammo for current testing and performance numbers is 36.50 H20 to case mouth at minimum case 1.672 at the SAAMI trim to 1.676 it would be more although I have not measured it yet as the other is my trim to.   I didn't realize the Kramer had a 31.5 capacity as the largest 5.56 case I had seen listed had 30.6 H20 capacity.  Then I realized I forgot to take into account the increase in the diameter of the neck as that would give it more H20 although that would be taken up by the larger bullet.  To keep a COAL of 2.26 the bullet will have to set deeper into the case as it is longer then the SPC.  This would increase the deficient even more.

Bigger bore, go with faster powders.The Spc may always come out on top d/t more case capacity but when it comes to efficiency it still has more of a "bottle neck".

ETA- think of the rifle as a single stroke motor.As the piston goes through it's only stroke , the "power stroke" it races to the end of the barrel(TDC).If you have to burn less fuel you'll need one that burns faster.This will generate more pressure but the bolt and chamber are thicker because the cartridge is smaller.I also believe the pressure curve would be more forgiving d/t the larger "combustion chamber " created by the cartridge-bbl interface.

ETA-1)forget about the creator pushing for military acceptance , this is the ar variant forum.
     2)forget about "it's been done before" , maybe between 1969-1979 but we have better and more selection of components now.
     3)no fireforming,size and trim.Same bolt ,cheap brass, and mags with minor mods.
     4) P-mags already openened up for 5.56 variants up to .30 cal would be cool.

Quoted: Quoted: Not to change the subject but has anyone considered necking down the 6.8spc to 6mm or 5.56mm? Yup, the 5.56X42 DMR and 6x41. See AR15 Performance

This particular cartridge actually looks more like an improved .270/6.86 ARC.

-ETA-it looks as if the 6.86 ARC has similar stats despite less case capacity and a slightly heavier bullet.This UCC must be at least the equivalent and positioned against the 5.56 and 7.62x39 would be a clear winner in many aspects.Much better sectional density and velocity  than the 7.62 and way more energy than the 5.56, a solid 200 yd(2000fps/1000ft/lbs) performer.This round certainly meets the criteria for an assault round.
-ETA2- I would take this round for the troops and add a DMR to every squad with an ar10/m14 in .260 Rem.There would be alot less people getting back up.

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

I wonder if it would work out of a 6.8 spc mag with a 5.56 follower?