Hi, all.

During the last two range sessions with my AR-15 I noticed that the bolt is locking back now and then when 1 round is still left in the magazine. It doesn't happen all the time, perhaps 15% of the time. And it only happens with a single round left in the magazine.

The issue does not appear specific to a specific magazine. It has happened with both a Magpul 10-round and 30-round magazine. These are my "range mags" that I use a lot, but I am far from a high round count shooter. I will try a USGI mag next time I go and see what happens.

Last time I came back from the range I made sure that the magazine catch moved freely in the lower, and all seemed well. The lower is clean, but I have never cleaned down inside the magazine catch slot. What steps would you suggest I take to troubleshoot and diagnose the issue? What are the possible causes and how would each cause be fixed?

BTW... this is a BCM complete factory upper and lower.

Thank you for your time!

Chris

This message has been edited. Last edited by: Chris17404,

Is the bolt catch under spring tension? Separate the lower from the upper and insert an empty mag, then insert a mag with one round and observe the bolt catch.

Hi, Chris. I performed the check you suggested. No, it looks like the bolt catch is not under spring tension. It jiggles rather freely. When I press on the lower portion of the bolt catch (the small tab used to manually lock the bolt back), the bolt catch easily jiggles up and down. Perhaps the spring broke. What is the procedure for replacing the spring? I have a BCM factory lower parts kit so I should have a replacement spring.

You have to drive out the pin holding in the bolt catch to change the spring.

The hole in the receiver is blind, the spring is loaded in, the plunger placed on top, and the bolt catch piece is placed in the slot over the hole and a cross pin is driven through the lugs on either side of the bolt catch to hold the assembly in place. The spring tension holds the bolt catch in the disengaged position until lifted by the follower of the magazine.

There are a few options for inexpensive bolt catch roll pin punch sets that have the handles half-cut to allow them to fit closer to the face of the receiver. Brownells has a set. Wheeler makes a rubber coated version. I don't have experience with any others. There are a few specialized tools, and some people prefer using a Knipex plier to drive roll pins.

You'll likely add a new ding in the finish of the receiver, if that matters to you. Having some aluminum black on hand is handy for quick touchup on anodized aluminum.

A suggestion to help minimize marking your receiver is to put two layers of black electrical tape by the hole where the roll pin goes into the receiver. I do this when driving pins in - never had to remove one.

PC

quote:

Originally posted by PCWyoming:
A suggestion to help minimize marking your receiver is to put two layers of black electrical tape by the hole where the roll pin goes into the receiver.

Painter's tape/masking tape works too, and leaves less adhesive residue once removed.

Thank you, everyone, for the info! I do believe I have one of the specialized bolt catch roll pin punch I got years ago but never used (never had the need). Now I do! I'll try your suggestions and let you know how it goes.

Easy fix! To make it even easier, only drive the roll pin out far enough to remove the bolt catch.

I’m also guessing that the spring isn’t broken, but rather the plunger developed a burr and is stuck. That might be a challenge to remove!

Yes, Chris. You’re exactly right. The plunger is stuck and it won’t budge, keeping the spring compressed. I am stumped. Any suggestions how to move this plunger? There’s no way to get ahold of it.

The plunger can move. I can press it in further but it only comes back out so far, flush with the receiver. It’s like the receiver itself has a little dent or burr that’s preventing it from moving it’s entire travel.

Issue solved! I fixed it as exactly explained in this thread:

https://forums.brianenos.com/t...catch-plunger-stuck/

Mine was the same exact issue. Thanks again to everyone for their assistance.

And note that an opened paper clip makes a very nice slave pin for aligning the bolt catch to hammer the pin back into place.

This message has been edited. Last edited by: Chris17404,

I've inexpertly painted mine in, used acetone to clean out the channel and got it working.

This cause is now something to check if assembling our own, as a preventative. Good tip.