For those of you who started with rifle length gas systems on their 6.5CMs and later changed to barrels with +2” gas ports, how dramatic was the difference in brass condition between the two gas port lengths, and were you able to lighten up the carrier or buffer mass with the +2” gas port to cut down on reciprocating mass and still have the brass come out in relatively good shape?
I have a pair of 6.5CM JP LRP07s, one 20”, one 22”. These were purchased about 10 years ago in the infancy of companies building 6.5 CM AR10s and at that time nobody was making barrels with +2” gas port locations. (I also had a 6.5CM GAP10 during that same timeframe, and it had issues piercing primers like crazy even with factory loads because the large firing pin GAP shipped it with didn’t play nice with 6.5CM. After 2 trips back to GAP they swapped the bolt for an Armalite bolt with a small firing pin and the piercing issue went away.)
I’ve always dealt with ejector swipes on these 2 uppers even with mild loads of H4350 or RL16 and 123gr Scenars. I’m 90% sure it’s because of the rifle length gas port not playing nice with elevated port pressures generated by the common 6.5CM powders with slower than typical 308 powder burn rates, and premature bolt unlocking and movement because of that.
Right now both are set up with LMOS carriers, adjustable gas blocks, and JP SCS buffers with 3 tungsten weights to try and delay/slow the bolt unlocking. JP initially shipped them with 1 tungsten / 2 steel weights on the buffer and the swipes were pretty bad. I then tried 2 tungsten / 1 steel which improved things a bit, and am now running 3 tungsten which improved brass condition a bit more. Gas block is set to just barely lock back on the last round. The brass comes out in pretty decent shape with 3 tungstens, but still not as good as I’d like (certainly not as good condition as brass from my old Armalite AR10 in 308.) Felt recoil from cycling isn’t bad, and the rifles don't “nosedive” excessively when chambering a round even with the H3 equivalent buffer weight slamming closed.
I run cheap Hornady 6.5CM brass that I usually buy once fired off the PX here and usually toss it after 4 trips through the ARs. Even with the 3 tungsten weights in the buffer sometimes I have to take a file to the ejector swipes before I resize the brass.
Debating if I want to swap these barrels out to new +2” gas port barrels before their end of life, or just run them as is until they’re shot out; they’re both very accurate so I’m not in a hurry to toss them. I suppose I could also sell the current uppers complete and buy 2 new complete uppers with +2” gas ports using the newest design JP semi-monolithic uppers with the integrated handguard mount… but that seems silly just to improve brass condition. The current uppers are very accurate, and I can buy a lot of Hornady 1x fired brass from the PX and toss it every 4th firing before the money saved by getting a few more reloads out of the brass would cover the cost of 2x new +2” gas barrels and 2x longer handguards or 2x new complete uppers from JP.
Appreciate any input and experience you've gathered going from rifle length to +2” gas port location.
I have a pair of 6.5CM JP LRP07s, one 20”, one 22”. These were purchased about 10 years ago in the infancy of companies building 6.5 CM AR10s and at that time nobody was making barrels with +2” gas port locations. (I also had a 6.5CM GAP10 during that same timeframe, and it had issues piercing primers like crazy even with factory loads because the large firing pin GAP shipped it with didn’t play nice with 6.5CM. After 2 trips back to GAP they swapped the bolt for an Armalite bolt with a small firing pin and the piercing issue went away.)
I’ve always dealt with ejector swipes on these 2 uppers even with mild loads of H4350 or RL16 and 123gr Scenars. I’m 90% sure it’s because of the rifle length gas port not playing nice with elevated port pressures generated by the common 6.5CM powders with slower than typical 308 powder burn rates, and premature bolt unlocking and movement because of that.
Right now both are set up with LMOS carriers, adjustable gas blocks, and JP SCS buffers with 3 tungsten weights to try and delay/slow the bolt unlocking. JP initially shipped them with 1 tungsten / 2 steel weights on the buffer and the swipes were pretty bad. I then tried 2 tungsten / 1 steel which improved things a bit, and am now running 3 tungsten which improved brass condition a bit more. Gas block is set to just barely lock back on the last round. The brass comes out in pretty decent shape with 3 tungstens, but still not as good as I’d like (certainly not as good condition as brass from my old Armalite AR10 in 308.) Felt recoil from cycling isn’t bad, and the rifles don't “nosedive” excessively when chambering a round even with the H3 equivalent buffer weight slamming closed.
I run cheap Hornady 6.5CM brass that I usually buy once fired off the PX here and usually toss it after 4 trips through the ARs. Even with the 3 tungsten weights in the buffer sometimes I have to take a file to the ejector swipes before I resize the brass.
Debating if I want to swap these barrels out to new +2” gas port barrels before their end of life, or just run them as is until they’re shot out; they’re both very accurate so I’m not in a hurry to toss them. I suppose I could also sell the current uppers complete and buy 2 new complete uppers with +2” gas ports using the newest design JP semi-monolithic uppers with the integrated handguard mount… but that seems silly just to improve brass condition. The current uppers are very accurate, and I can buy a lot of Hornady 1x fired brass from the PX and toss it every 4th firing before the money saved by getting a few more reloads out of the brass would cover the cost of 2x new +2” gas barrels and 2x longer handguards or 2x new complete uppers from JP.
Appreciate any input and experience you've gathered going from rifle length to +2” gas port location.
