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I just received the same barrel as you from FA. Iordered it and and a 12" FF tube dpms heavywall upper and chrome carrier and bolt. Fulton checked headspace before they shipped it all. I did get a chance to task with a smith there about what they do to make the feedind/chambering smoother to help save brass from chewed up shoulders. they told me they do some polishing/grinding on the center bottom lug and take the edges down(radius them). I talked to gunsmith friend that builds ar-15 &ar10. He suggested grinding down the leading edge of the center lug and the ridge that runs up it to the tip of the lug, but not to change the height of the lug in the barrel extension. this was easily accomplished with a dremel and a small stone. I broke the edges with a real fine sanding drum, nothing crazy, just taking the edge off. it feeds great and the sharper shoulders of the cm round is not chewed up at all, much less then the original cmmg does to 308 brass. I was really beginning to think the ar10 was just too hard to shoot. I shoot br and have no problem holding aggs in the hi-middle.1s. I just could not get that cmmg sass to shoot no matter what load I tried. I was at the verge of selling it and probably would have but none of the area shops were interested in a heavy barreled ar10. I have a geissele match trigger set up at 1.75lbs 1st stage, 14 oz 2nd stage, it was in there when it was a 308 and is still in there now. The good news is the cmmg barrel was crap, 1.5 moa was best it could do with a random shot thrown out here or there that could not be blamed on enviro or shooter. I feel vindicated in my skill as a shooter as the initial load development resulted in 3 out of 5 different loads going under .5" at 100 from prone bipod/rear bag. my barrel really liked 123 amax, 44.0 and 44.5 gr h4350 and bullets set to mag length resulted in a .378" and .421" 5 shot group. 140 bthp hornady match and 42.4 gr h4350 shot a .471" 5 shot. This was during initial break-in. after 25 rds cleaning at 5 rds, shoot 10 and clean, shoot 10 and clean. Barrel cleans up real good with little to no trace of copper, I use kg1 for carbon and boretech eliminator for copper. Numbers over the chronograph were lower then my two 26" bolt guns, but that was expected. the 123 amax/44.0 was 2877 with sd of 7.84. 123amax/44.5 was 2907 with sd of 14.23. I built a savage 10 tact with a shilen select match 26" 6.5cm barrel and happened to have it on hand when I was at the range that day, thought I would try it's load in the gasgun. That load is 42.4/140amax at 2.210from the ogive which is mag length in the magpul lr-20 mags. This grouped awesome, i did shank the last shot, but the first 4 rds cut a .274" oblong in the paper.

Got a cmmg 308 that is real ave shooting and plan to swap barrel to a 6.5 cm 24" from Fulton and use their fft. Would the dpms wrench work, i read that the armalite pegs can be all removed but two and it will work with a Fulton fft. Just not sure what wrench for the cmmg nut. Thanks in advance