This has been my experience as well with 4x 6.5CM AR-10s… 1x being a home built, 1 GAP-10, and 2X JP’s. After about 50 rounds the bolt head will start getting sticky in the carrier and start causing occasional malfunctions as well as making the bolt difficult to run manually. The “stickiness” consistently occurs regardless of lube-- light grease on the gas rings, oil on the gas rings, or run dry. When it starts getting sticky a couple drops of oil dripped into the 2x vent holes in the carrier and it will free up and run smoothly for another 40-50 rounds before getting sticky again. All 4 rifles exhibit this behavior.
My hunch is the typically slower burning powders like H4350 and RL16 used in 6.5CM ammo leave more deposits in the bolt, carrier, and gas rings causing the issue. My 308 AR-10s never had this sticky bolt issue even after 200+ rounds, but 308s typically use faster burning powders, so my thought is the faster powders typically used in an 308 AR-10 are pretty much fully combusted by the time they get to the gas port and thus don’t deposit as much “stuff” in the bolt and carrier. What makes me think the usual 6.5CM slower burning powders are a contributing factor is for a while I tried running AR-Comp in the 6.5CM and the “sticky bolt” issue stopped. AR-Comp is a much faster burning powder than H4350 or RL16. I did end up switching back to H4350 & RL16 though as you can get much, much higher velocity out of them before running into pressure signs compared to AR-Comp, and when I switched back to H4350 & RL16 the “sticky bolt” issue came back.
Not sure how much the new +2” XL-length gas systems will help with the “sticky bolt” issue with 6.5CM rifles, but my hunch is that it will help (along with improving brass condition from reduced gas pressure on the bolt making the cycling gentler compared to the shorter gas system.) All my 6.5CM AR-10s were/are standard 308 rifle length gas systems, the trend to start using the +2” “XL” gas systems in the 6CM / 6.5CM rifles started a few months after I bought my last JP.
Interested to hear from others on this issue...
