Ar-15 bolt won't hold open

[triceratops3]

I just recently picked up a used ar-15 build and the bolt wont hold open after the last round. And trying to figure out what I should do to troubleshoot it.

It is built on a mega arms billet upper and lower with I believe a DMPS lpk. It has a 16" barrel and a carbine length gas system.

I'm using some reloads that have proven reliable in other ar's. The bolt held open maybe 6/20 or 25 times. I'm also using pmags. and it holds open every time when operated using the charging handle.

What does everyone think could be the problem?

I appreciate any help.

Thanks.

 

[Why1504]

Do the mags work in the other AR's 100%?

 

[MarkCO]

Worn gas rings, misaligned gas tube, misaligned gas block, mag catch needs one more turn inwards.

 

[bigmatt17073]

I would try a few things to trouble shoot. Try some factory loads just to be sure in some other mags (GI maybe) to see if that works. If not there is an issue somewhere with the gas. It isn't getting enough and short stroking. Clean the gas tube, check to make sure the gas block is aligned with the port and tight, and check the gas key on the BCG. I had slightly loose gas key that was causing those issues and some FTE as well. I snugged up the bolts and hasn't given a problem since. A heavy buffer and spring could also do it with the gas not having enough force to move the BCG far enough rearward for the bolt catch to engage.

 

[triceratops3]

Why1504: mags have worked 100% in other ars.

MarkCO: I'll check those. One question though, how would I check the gas rings and what should I look for?

bigmatt17073: I'll try factory ammo and another mag. I will also check everything over. Question: are you saying I should see if I have a heavy buffer/spring?

Thanks for the replies so far.

 

[bigbear_98]

bolt catch needs one more turn inwards.

How do you do that?

 

[MarkCO]

How do you do that?

Use a punch, push the mag release in far enough that the catch protrudes and turn it inward one revolution.

 

[bigbear_98]

Use a punch, push the mag release in far enough that the catch protrudes and turn it inward one revolution.

Is that not the mag catch and not the bolt catch? Bolt catch is pinned on the side and has a spring and detent under it to keep it out of the way of the bolt, No?

 

[MarkCO]

One question though, how would I check the gas rings and what should I look for?

Pitting and erosion, even bending at the edges where they would contact the bore of the carrier.

 

[MarkCO]

Is that not the mag catch and not the bolt catch? Bolt catch is pinned on the side and has a spring and detent under it to keep it out of the way of the bolt, No?

Yes, I am an idiot. I changed my post. YES MAG CATCH.

apologies to the OP if I confused you.

 

[bigbear_98]

Why1504: mags have worked 100% in other ars.

MarkCO: I'll check those. One question though, how would I check the gas rings and what should I look for?

bigmatt17073: I'll try factory ammo and another mag. I will also check everything over. Question: are you saying I should see if I have a heavy buffer/spring?

Thanks for the replies so far.

I was taught to take the bolt carrier out, pull all of the pins out and take the bolt and carrier apart. Clean it all up, put it back together without the pins and hold it by the bolt, bolt up, carrier down. Shake it up and down a little. If the carrier can fall off without much pressure the gas rings are bad.

 

[triceratops3]

Yes, I am an idiot. I changed my post. YES MAG CATCH.

apologies to the OP if I confused you.

Thanks for the info and clearing that up. I'll double check everything to see if it's all aligned and in good condition.