Gunsmithing AR-10 Firing pin fouling

[Teamworksetd]

I have a AR-10 in 6.5 creedmoor and I can get about 30 rounds through it before it stops shooting well. The bolt head gets so sticky that I cant move it forward by hand. When I disassemble everything and clean it thoroughly I can get another 20-30 rounds before the same thing happens again. When I clean it the firing pin has more fouling on it than I have ever seen in any of my AR-15s. I have gone through this process three times now and the same result each time. I am wondering what the cause might be and what the fix is. Wondering if the gas rings are bad and causing excessive fouling. I have order new gas rings but they haven't gotten here yet. I do run it very wet and well lubed.

Any help would be appreciated

 

[Teamworksetd]

Addition - I have checked the firing pin and it is not bent.

 

[loveha]

You aren't putting any lube on the firing pin are you?

 

[Teamworksetd]

You aren't putting any lube on the firing pin are you?

No, I do not lube the firing pin. I do lube the gas rings though.

 

[loveha]

You aren't putting any lube on the firing pin are you?

No, I do not lube the firing pin. I do lube the gas rings though.

Not saying that is your problem, but those shouldn't really be lubed either.

What is your lube of choice?

 

[Teamworksetd]

Hoppes #9 gun oil

 

[Kiba]

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...

 

[FisherT&C]

I think the Tin and Nickel Boron coated assembly groups are worth it for cartridges like the Creed's

 

[FCS]

Remnants from mobil 1 0-30, 5-20 and 10-30 after oil change on vehicle(s) go into flip top bottle.
Wet lugs, wet rails on BC, wet gas rings with light film of oil. Wet a cotton tipped, wood stem applicator and apply to surfaces.
Several hundred rds suppressed is norm. Unsuppressed goes longer w/o need to add lube.
LT PredatOBR / UUK, GAP, Armalite, home built, mix of carrier finishes.

 

[Teamworksetd]

The BCG is Nickel Boron.

Never thought about using old oil but will give that a try. Thanks for the tip.

 

[FCS]

The BCG is Nickel Boron.

Never thought about using old oil but will give that a try. Thanks for the tip.

New oil, just stand “empty” mobil one bottle in funnel, funnel into my flip top bottle. Only some small portion of an ounce left but not worth me waiting to put into engine.

 

[Teamworksetd]

New oil, just stand “empty” mobil one bottle in funnel, funnel into my flip top bottle. Only some small portion of an ounce left but not worth me waiting to put into engine.

Got it. Thanks for the clarification.