6.8 Upper Recommendations

[husker_t]

Back to the original poster's question, I have two responses:

1. For varmint, you don't use 6.8 spc. It's relatively rare, and relatively expensive, and it's not a traditional varmint caliber. Use a true varmint caliber, and your top two choices (in the sense of what is most widely used and also available in standard AR's) are: .223, .204.

2. If you decide that you do still want a 6.8 spc anyway, get the Kotonics upper. And try to get one with a 1:11 twist barrel, and an SPC II chamber if possible. Kotonics makes those. I don't have time to go into a lot of details, but this has been a recent development in 6.8: they're coming out with some improved ammo, but many of the 6.8's on the market cannot shoot it well because of issues with pressure (due to the chamber) and the performance (due to the twist rate). You can get more info from this post at AR15.com:

AR15.COM :: Forums :: 2008 6.8 SPC AMMO AND BARREL TWIST RATE TEST


(For the convenience, here are the CONCLUSIONS from the above article about 6.8 testing and the use of the SPC II chamber and 1:11 twist barrels, but you really should read the whole post at AR15.com):

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Our conclusions
[Husker_t note: the conclusions about their tests on various 6.8 ammo and barrels]:

1) 1:11 inch twist appears to be one of the most important factors in ameliorating high pressure of hot 6.8 SPC loads. 1 turn in 10 inches is unnecessarily fast with the current 6.8mm bullets, including 130 grains, and it offers no advantage over slower twists. 1:10 twist may exhibit higher pressure than barrels of slower twist, and thus may limit the performance of the cartridge significantly.

2) SPC II and DMR chambers are somewhat important in ameliorating pressure, but may be less a factor than the twist rate.

3) The 6.8 SPC will achieve the highest velocity, safely in SPC II or DMR chamber if paired with 1:11 or 1:12” twist. This combination, were it to become the standard, could allow ammo manufacturers to increase the performance of the 6.8 SPC substantially. Most current factory ammo is loaded to accommodate the SAAMI chamber and 1:10 twist, rendering it with reduced performance.

4) The 6.8 SPC may be capable of achieving high velocity in SAAMI chambers, but probably most safely when paired with a 1:11” or slower twist rate.

5) There seems to be little reason for manufacturers to continue to make 1:10” twist barrels in 6.8 SPC. SBR’s may be the exception, but we fail to see how a 1:11” twist could be a disadvantage in barrels longer than 11 inches, with bullets ranging from 90 to 130 grains. We do not yet have any opinion about pistol length barrels because not enough testing has been done.

6) A suppressor could potentially tip your max loads over the edge of the pressure safety margin, even if you have a 1 in 11” twist, DMR or SPCII chambered gun.