astrohog

I do not have experience with the blackout, but the general "internet" consensus is that it is best at subsonic/suppressed. The only complaints I have heard about the x39 is the lack of hunting bullets and the case head is large causing broken bolts in AR15's. The grendel and spc are neck and neck, but the .mil has done lots of testing on the 6.8mm bullets and they have better terminal performance than the 6.5mm bullets. check this out: http://www.dtic.mil/ndia/2008Intl/Roberts.pdf pg14 has a some good info on the 6.5, x39, and 6.8.

I use the 6.8 SPC for hunting Whitetail. Killed two ~120lb deer with the Hornady 120 SST. First one was hit in the top of the heart and only went about 30yds, and I spli the heart into 3 pieces. The other was a double lung and there was a very good blood trail and it went about 50yds. Both were shot at about 75yds. Check out 68forums.com if you want more information this round. The consus is that the 6.8 spec 2 chamber is better than the SAMMI chamber and that either chamer is good on whitetail out to 300yds. 68forums has a hunting section and some guys are using it for elk and caribou.