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(Solved) AR-15 issue: bolt prematurely locking back with 1 round left in magazine Login/Join 
Domari Nolo
Picture of Chris17404
posted
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,



 
Posts: 2162 | Location: York, PA | Registered: May 17, 2006Reply With QuoteReport This Post
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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.


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Posts: 8605 | Location: UT | Registered: December 05, 1999Reply With QuoteReport This Post
Domari Nolo
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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.



 
Posts: 2162 | Location: York, PA | Registered: May 17, 2006Reply With QuoteReport This Post
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Picture of Rustpot
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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.
 
Posts: 5989 | Location: Romeo, MI | Registered: January 03, 2009Reply With QuoteReport This Post
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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
 
Posts: 1128 | Location: NW Wyoming | Registered: November 23, 2014Reply With QuoteReport This Post
Fighting the good fight
Picture of RogueJSK
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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.
 
Posts: 28994 | Location: Northwest Arkansas | Registered: January 06, 2008Reply With QuoteReport This Post
Domari Nolo
Picture of Chris17404
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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.



 
Posts: 2162 | Location: York, PA | Registered: May 17, 2006Reply With QuoteReport This Post
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Easy fix! To make it even easier, only drive the roll pin out far enough to remove the bolt catch.


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Posts: 8605 | Location: UT | Registered: December 05, 1999Reply With QuoteReport This Post
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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!


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"Owning a handgun doesn't make you armed any more than owning a guitar makes you a musician." -Jeff Cooper



 
Posts: 8605 | Location: UT | Registered: December 05, 1999Reply With QuoteReport This Post
Domari Nolo
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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.



 
Posts: 2162 | Location: York, PA | Registered: May 17, 2006Reply With QuoteReport This Post
Domari Nolo
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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.



 
Posts: 2162 | Location: York, PA | Registered: May 17, 2006Reply With QuoteReport This Post
Domari Nolo
Picture of Chris17404
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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,



 
Posts: 2162 | Location: York, PA | Registered: May 17, 2006Reply With QuoteReport This Post
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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.
 
Posts: 606 | Registered: December 14, 2021Reply With QuoteReport This Post
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