AR function problem

[Farnham]

I took my newly built AR-15 to the range this weekend, and encountered a problem I've never seen.

I fired one round, and the bolt appeared to only partially unlock. It moved back about the same distance as the bolt moves in the carrier, and FROZE. I had to remove the upper and yank back the charging handle to get the spent cartridge to eject. This happened several times (a couple times, it froze so hard, I had to slam the charging handle into the bench to eject the shell).

When I stripped the rifle down, I noticed an extremely worn spot on the bolt cam pin (keep in mind, these are all new parts). When I'd "flip" the fully assembled bolt carrier, the bolt would slide out, and when I hit it to push it back in, it'd hang up.

Anyone ever see this? I think the bolt cam pin is out of round, or the slot in the bolt carrier isn't cut right. Any opinions?

S/F

Farnham

 

[rbernie]

Lube the snot outta the bolt and try it.

 

[rero360]

you wouldn't happen to have any pics of this would you? I'm trying to picture it in my mind, can't, are you saying the bolt is staying in place and the carrier is moving backwards, or vice versa, because if its the bolt moving and the carrier staying put could be a blocked gas tube, if the bolts stuck and the carrier is moving then probably would be a super tight bore or the bolt isn't unlocking completely

I'm not completely sure, these are just from the top of my head, could be something else, probably is, but thats my .02 cents, hope I could help.

 

[rbernie]

When I'd "flip" the fully assembled bolt carrier, the bolt would slide out, and when I hit it to push it back in, it'd hang up.

Sounds like the bolt is hanging up in the carrier. This could be a parts mis-match issue, and it could simply be a lack of lube on new (as-yet-un-mated) dry parts.

If you can get the bolt to snap in and out if lubed, run it like that for a bit. If not, then yes - look to the carrier/cam pin/bolt fit....

 

[dmftoy1]

I don't know if this could be your cause or not (SWAG) but you might check the gas rings on the bolt and make sure that they've not somehow they've all become aligned. I've never seen it happen but I read about it on the internet once. (ar15.com)

Have a good one,
Dave

 

[Farnham]

I did start out with just a very light coat of CLP on the bolt, so I tried the "lube the snot out of it" approach while I was there, and thought it worked, I went through one mag just fine. Then it started happening again. :banghead: Guess I'll try it again. I think you're right, rbernie, probably just need to break everything in and keep it well-oiled while doing so.

No pictures (stupid batteries), but I realized my description was sorta vague on which part was moving. It appears that the bolt carrier was moving back, and the bolt was trying to unlock, but would hang up after only partially unlocking (now that I describe it better, I can see how the cam pin failing to move smoothly in the bolt carrier could definitely cause that, as well as accounting for the worn spot on the cam pin).

dmftoy1, I've also heard about the gas ring alignment thing (I think it was in boot camp) so I checked while I was at the range, and that wasn't it. Nice SWAG though!

Thanks for the replies.

S/F

Farnham

 

[NMshooter]

Bolt cam pins are cheap.

Any worn spots elsewhere?

Unfortunately, bolt carriers are not cheap, hope yours is OK.

Incidentally, is your carrier key staked?

 

[hksw]

Although I can't offer any significant insight on the problem, I think I can make a suggestion on the field clearing problem. It is situations like this that I keep a plastic/rubber headed hammer in my gun tool box which I bring with me every time i go out shooting.

I had a similar lock-up. I was shooting crappy NPA ammo through my plate shooting AR and it was not dimensionally correct and locked up the action with the round unfired. Pulling on the handle was very difficult exacerbated by the small two finger size of the handle (got a blister trying to pull the handle back) and keeping the rifle pointed downrange. Enough of the carrier was still in the lower to prevent the halves from coming apart. Luckily, I was the only one on the 50 at the time. Got out the hammer and tapped the non-lever side of the handle with the plastic side of the hammer (I'm sure the rubber side would have worked too) and the bolt loosened no problem. Had to use it a few more time in trying to burn up the NPA.