Bolt (Lock Open)

[One Shot, One Dropped]

I have searched, but I can't find a solution to a what seems like a simple problem I have.

One of my ARs will not lock the bolt open/back after the last shot.

I have tried:
thorough cleaning
different magazines
different ammo

It will lock back if I leave a magazine in and pull the latch back.

Otherwise, it cycles just fine.

It has about 200+ rounds through it.

By the way, it is a bushmaster upper on a High Standard lower with a RRA Standard Lower Parts Kit (I don't think any other information is necessary).

Any help would be appreciated.

[Dirtbiker]

Short stroking

Check to see if the gas rings on the bolt are lined up. They should not be.

Try a different brand of magazine follower.

Heavy bolt, buffer, too stiff buffer spring?

[Linus]

+1 on the heavy buffer spring.

[One Shot, One Dropped]

I tried the different follower, and it didn't work out. I'll try checking the gas rings , and, hopefully that will work out.

I'll probably have to do that later because my brother is taking a little nap (he needs to grow up), and I don't want to startle the crap out of him.

[Beelzy]

I agree with the buffer spring suggestion.

[One Shot, One Dropped]

What would I do, though? Would I just replace it with a lighter spring?

Funny thing is, I didn't assemble the gun, I bought all the parts and had it assembled by a dealer so that, once the 10 days were up, I could shoot within minutes.

If it's a bad spring, I will just take it back to them.

[50BMGBOB]

My first OLL did this. I checked the buffer spring but that didn't help. I got a friends upper and it worked fine with my lower started swapping parts and it finally narrowed it down to the bolt carrier. Got it fixed now. Funny thing, that was my Armalite AR15T upper. If you have another AR you could swap parts to narrow it down.

[bigthaiboy]

My first OLL did this. I checked the buffer spring but that didn't help. I got a friends upper and it worked fine with my lower started swapping parts and it finally narrowed it down to the bolt carrier. Got it fixed now. Funny thing, that was my Armalite AR15T upper. If you have another AR you could swap parts to narrow it down.

Just curious. What was the problem with the bolt carrier, and how was it repaired?

[bigdave1121]

Maybe technique should chime in here. Afterall, the rifle was assembled at his store

[randy]

More oil? Get it good and wet. Shoot some xm193 and see if it locks open. More oil in the bolt not just the carrier.

[THE 0NE]

bring it in i will fix it its no problem..... did it lock back in the first place or did it just start after awhile?

[MFortie]

Mine did the same thing after I assembled it. Turns out the bolt catch wasn't moving freely -- I did a little judicious stoning on the bolt catch to relieve the binding to get it functioning (somewhat) for a class.

After I replaced the catch with an ambi catch, it works just fine. So my assumption is an out of spec bolt catch.

Also, pulling the trigger on a cocked lower without the upper can hammer the channel where the bolt catch rides and cause binding (not to mention eventually crack the lower.)

[bigdave1121]

bring it in i will fix it its no problem.....

That's what I told him to do

[technique]

Quick fix, not a problem.

[One Shot, One Dropped]

bring it in i will fix it its no problem..... did it lock back in the first place or did it just start after awhile?

I don't remember it ever locking back. I'll bring it in. The only reason I resisted is that it's a mad detour to come down there (I don't even get on the freeway when I go to the range, when I decide not to shoot at the house that is), and I always have trouble coming to see you guys and not leaving with another gun DROSed. Well, maybe I'll just have to do that.