Minor problem with my AR

[ChamberedRound]

I took my Bushmaster M4gery out to the range on Friday, and had a minor problem: The bolt wasn't holding open after the last round. I was trying a set of windowed PMAGs for the first time, and after I got home wondered if the mags could be the problem. In the past I've shot GI mags and not had this problem, but on this day I didn't shoot the GI mags to compare. In addition to the mags, the gun hasn't been field-stripped and cleaned in awhile (probably 500 rds or so). I put about 100rds through it without any other problems; it ran fine otherwise.

So, anyone have any ideas as to why the bolt didn't hold open? Could it be the new mags, that the gun wasn't clean, both, or some other mechanical failure which I may need to check and service?

Thanks in advance for any advice.

[NightRocker]

This just came up today earlier, http://forum.pafoa.org/rifles-42/298...ems-my-ar.html

[ChamberedRound]

This just came up today earlier, http://forum.pafoa.org/rifles-42/298...ems-my-ar.html

It didn't just come up there today, the thread you reference is one which started over a year ago, and aside from the last 2 posts hasn't been updated in awhile.

Also, the problem in that thread related to failures to feed and eject, neither of which are problems I'm having; BHO is the only issue for me. The information there is good, but I was hoping for some other information, i.e. are BHO problems a common issue on the AR platform? Does the problem require more than routine maintenance, like parts replacement? Is it sensitive to the magazines used? I'm confused because I tried what are touted as some of the best mags on the market, yet had a problem.

[NightRocker]

The bolt catch spring only holds the bolt catch clear of the bolt. A weak spring will cause the bolt catch to rise up during firing and lock the bolt back. A spring that is too strong could conceivably hold the bolt catch down, preventing lock-back. (Unlikely)

Weak mag springs can cause failure to lock-back. Check with empty mag and pull the charging handle back.

Short-stroking is another cause. Load 1 round in the magazine and fire. Repeat a few times to confirm consistent bolt lock-back.

Out-of-spec bolt catch can cause the the catch to move to slowly. Check for free movement.

[Legion_Prime]

It didn't just come up there today, the thread you reference is one which started over a year ago, and aside from the last 2 posts hasn't been updated in awhile.

Also, the problem in that thread related to failures to feed and eject, neither of which are problems I'm having; BHO is the only issue for me. The information there is good, but I was hoping for some other information, i.e. are BHO problems a common issue on the AR platform? Does the problem require more than routine maintenance, like parts replacement? Is it sensitive to the magazines used? I'm confused because I tried what are touted as some of the best mags on the market, yet had a problem.

Wow damn, I didn't realize quite how badly that guy had necroposted. Hahaha

PMAGS in a BM, while weak magazine springs could cause your problem I'd say with both of them new, the problem's more likely in your rifle. I'm guessing that the mag catch is binding. Nightrocker has covered pretty much all the bases to check to figure out what's going wrong. I would only add to insert an empty mag with the rifle shotgunned, you will be able to watch the bolt catch to see if it binds or (highly unlikely) if the mag catch is out of spec and doesn't hold the magazine up high enough for the follower to positively engage the bolt catch. Hope you get it sorted.

[ChamberedRound]

Thx for the advice guys. I'll try what you've suggested and let you know how it goes.

[Guns4Fun]

Just out of curiosity, what ammo were you shooting?

High power 5.56
or
something low power like wolf .223

[Steve-L]

I'm having the exact same problem with pmags on my Bushy and PWA lowers.

[ungawa]

If you were shooting Wolf or other cheap underpowered steel case ammo then that is probably either the cause or a contributer. My second guess would be the P-mags. Those are the first two you can rule out with ease with another trip to the range. 500 rounds without cleaning, not an issue.

[synergy]

Going light on the lube can do the same thing...slow the carrier down so that it doesn't cycle 100%.

I doubt the mags or the bolt catch itself are the problem.

Try it again with the same ammo, wet...then see what happens.