Some random thoughts on the terminal performance characteristics of some of the more common projectiles in 6.8 mm:
Barnes 85 and 110 gr TSX JHP -- These all copper, lead free bullets bullets offer good expansion and penetration. They would be useful as both an LE barrier load and for hunting medium game.
Hornady 110 gr VMAX PT -- This is a great fragmenting bullet and is perfect for CQB/LE SWAT entry work; it is also a good choice for light to medium game.
Hornady 110 gr OTM (loaded by Hornady) -- This is good fragmenting bullet for military use where PT bullets like the AMAX are prohibited, as it offers similar terminal performance to the 110 gr AMAX. It has better glass performance than the 115 gr OTM.
Hornady 115 gr OTM (loaded by Remington) -- This load has dominated recent military terminal performance testing because of it’s early yaw and superb fragmentation, even at reduced impact velocities.
Remington 115 gr JSP -- Good expansion and penetration make this an excellent choice for law enforcement use through glass and other intermediate barriers, as well as into vehicles. It is also an excellent choice for hunting medium size game.
Sierra 110 gr Pro Hunter JSP -- This is a good bullet for law enforcement use through glass and other intermediate barriers and would be a great load for Highway Patrol and State Police who are working primarily around vehicles. It is also a great hunting load for medium size game.
Sierra 115 gr OTM w/cannelure -- This second generation SMK offers improved feeding reliability and much more consistent terminal performance with early yaw and ideal fragmentation. It is a good choice for military combat and non-barrier LE use.
Sierra 115 gr OTM w/o cannelure -- This first generation SMK is very accurate, but offers somewhat variable terminal performance and is not a great combat, LE, or hunting choice--it is best suited for match target shooting.
X-Treme bullets 115 gr TMJ -- This bullet offers very good soft tissue terminal performance, however, like many FMJ and OTM loads, performance through glass is not great. There have been some issues with pressure spikes using this load in undersize chambers, as well as some dimensional variances.
With the projectiles discussed above, a 1/12 twist barrel is probably the best choice!
SSA has developed two true AP loads, a 97.5 gr tungsten penetrator similar to M993/M995 and another using a hardened steel penetrator like the old .30-06 M2 AP “black-tip”.
Note: Most of the 6.8 mm bullets are continuing to upset down to at least 2100 f/s
It is very important to keep in mind that the proper 6.8 mm velocity is 2600 fps +/- 50 fps for 110-115 gr projectiles when fired from a 16" barrel. Government organizations who purchase 6.8 mm should specify in their purchase contracts a minimum acceptable velocity of 2500 fps with an objective velocity of 2600 fps for 16" barrels firing the 110-115 gr projectiles. For duty use, flash suppressed powder, crimped primer, waterproofing, and bullet cannelure should be mandatory requirements.
Zak Smith has written the most comprehensive and accurate article on the history, genesis, and development of the 6.8 mm SPC that I have yet publicly encountered: http://demigod.org/~zak/archive/sgn_68spc.pdf
SSA 2nd generation 115 gr SMK OTM w/cannelure, 5 shot averages:
20” barrel: ave vel = 2561 fps; 10 fps extreme spread
16” barrel: ave vel = 2525 fps; 18 fps extreme spread -- lost 36 fps from 20"
12.5” barrel: ave vel = 2384 fps; 12 fps extreme spread -- lost 141 fps from 16"
10” barrel: ave vel = 2265 fps; 27 fps extreme spread -- lost 119 fps from 12.5"
7.5” barrel: ave vel = 2035 fps; 27 fps extreme spread -- lost 230 fps from 10"