(2004)Remington 6.8x43 SPC-(SAAMI)- has a .050 freebore and when submitted to SAAMI had the correct 45 degree cone angle, has a .278 diameter freebore. Some drawings from PTG has a 80 degree cone angle, no one knows where the error originated.
(Jan 2006)6.8 Remington SPCII-(SPCII)- has a .100 freebore originally drawn by Art of SSA or Barrett not known for sure had the correct 45 degree cone angle, has a .278 diameter freebore, .3085 neck. Some drawings from PTG has a 80 degree cone angle.
(2007)ARP 6.8x43 DMR (DMR)- has a .080 freebore, .277 dia and a .305 neck diameter it was designed to correct the bad 80 degree cone angle and be a little more accurate in stainless match barrels because of the shorter freebore and .277 dia leade. Only used in ARP stainless match barrels.
(2008)ARP DMR-C enlarged only enough to take into account the thickness of the chrome in the chamber, neck .0307/.3075-Used only in the chrome lined barrels we had produced in late 2008 and sold in early 2009
(2009) ARP 6.8- has a .080 freebore, .2775" dia with the correct 45 degree cone angle and a .3085/.309 neck to work better with the newer SSA brass size.
Noveske mod 1-no real idea, they say it has a .100 freebore, assume it is the same as the SPCII.
(2010) New SPCII- Ben with Bison posted a new SPCII drawing that shows a .114 long freebore with .278 diameter and the correct 45 degree cone angle, everything else is the same as the other SPCII.
IMO all of these chambers except the original "Remington 6.8x43 SPC"(SAAMI) will handle high performance ammo.
These chambers seem to confuse many possibly because the public has been exposed to the chambers and given more info than what has been released about the 5.56 and 308 chambers. There are 14- 308 chambers that I know about but most of the public thinks there are only 2 the 308 and the 7.62x51 NATO. There are at least 10 -223/.556 chambers that I know of. The 6.8 isn't different it is just that there is a lot more info being passed around to the public about it.
right now I think a new saami designation would confuse the caliber more--- we just need someone who will load factory ammo to spec II pressures and I think others would pick up on it if it sold well