AR 10 issue

[tacgnut]

I built an Ar10 last year and for some reason the carrier will not lock all the way to the rear after last shot. It will hang up on the magazine but as soon as you hit the mag release button, the bolt carrier goes forward once the mag drops.
The carrier will lock in the rear position if you manually use the bolt stop but will not lock in place after your last shot.

Magpul PRS/standard buffer
Gen II upper
Gen II mags
Gen I carrier
Custom upper
I built the lower

It doesn't make sense that the carrier would not fully cycle to the rear as this functions flawlessly. After the last shot, I have to manually pull the charging handle to the rear and then depress the bolt stop to engage.

Whats up?

 

[LoneWolfUSMC]

Re: AR 10 issue

Has it ever worked properly?

 

[ORD]

Re: AR 10 issue

Are you running the Gen 1 bolt catch? If so...the Gen 2 mags will not engage it properly and you will experience the problem you are describing (at least the problem I think you are describing).

See here:

Armalite Tech Note 71

 

[Eagle1899]

Re: AR 10 issue

What buffer are you using?

 

[Hellbender]

Re: AR 10 issue

As Lone wolf asked....Was it working right at one time?

You gas block may have slipped forward or moved a bit, partially blocking your gas port, reducing the gas available.

Check it.

Have you changed the load you are shooting?

 

[LoneWolfUSMC]

Re: AR 10 issue

Also, when you say you "built" the lower, are you saying you machined the lower? Or are you saying you put the parts in a manufactured lower?

 

[AXEMAN]

Re: AR 10 issue

hey i was reading up on buffers and heavier buffers for the 308s and a guy at heavybuffers.com mentioned that sometimes a few coils need to be clipped off the recoil spring to get the bolt catch to work properly. just thought id throw that out there...

 

[steelcomp]

Re: AR 10 issue

Look at the screw in the back of the PRS that attaches it to the extension. On mine, that screw was longer than it needed to be and not allowing full travel of the bolt, causing a short stroke. It may be just long enough for you that it's allowing regular cycling, but still not allowing lock up after the final shot. The screw is way longer than it needs to be, so cutting .100 off the end won't hurt a thing. Remember to not plug the hole in the end with a burr or something.

 

[MikeeBooshay]

Re: AR 10 issue

Had to cut almost a half inch off the screw holding my PRS on. Haven't shot it since, but the bolt catch hasn't been working lately, didn't really notice if it started when the PRS was installed.

Just start the screw in the extension, make sure the PRS is all the way forward. Then retract the bolt with the charging handle, and hold it back. Using your free hand, lightly run in the screw. When the screw contacts the rear of the bolt, that is max depth. Measure the length the bolt protrudes, remove bolt, and shorten it by removing the same amount that the bolt protrudes, plus a few, (like .050") thousandths to allow for tightening.

That should fix the long bolt, if that doesn't fix the short cycling also.

 

[bignada]

Re: AR 10 issue

There is a thread in the gunsmithing forum on tuning the AR bolt catch. Might want to look there. Guy cites that about .075" gap between boltface and magazine release is correct when charging handle is holding bolt all the way to rear....

http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=1986200#Post1986200


Hellbender knows his stuff...