Possibly the mag follower is not pushing the bolt stop far enough. Several factors at work here. A couple of things to look for. Bolt stop spring tension too strong. Mag spring too weak. Poor contact between the mag follower and the bolt stop. Magazine not seating properly.(check the OP rod spring guide) Or it could be as simple as the bolt stop being worn.

 

My SA M1A started doing this about 20 years ago. I fooled with it a bit by manually moving the bolt catch as far as it would move to engage the bolt and it would still slip off.

I got to looking and the bolt catch face was very smooth/shiny. I just assumed mine had worn smooth due to being softer than the bolt.

So I'm very careful with it. If I elect to run patches/brush through the barrel with the rifle assembled I use a magazine inserted into the rifle to insure the bolt doesn't slip off the bolt catch and slam forward.

 

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So I'm very careful with it. If I elect to run patches/brush through the barrel with the rifle assembled I use a magazine inserted into the rifle to insure the bolt doesn't slip off the bolt catch and slam forward.

You can also insert one of the 5-round stripper clips into the clip guide instead of using a magazine to hold the bolt from slamming forward during cleaning.

Cheers

 

I have seen non-USGI bolt catches mare and deform. The metal is not as hard. It looses it's ability to do it's job.

 

If it only does it with those mags, then the follower isn't properly pushing up the bolt catch.

If it does it will all mags, then the rear face of the bolt stop is worn or polished smooth. It happens a lot with USGI parts kits. Sometimes you can "rough up" the spot where the bolt stop contacts the bolt, but a new one may be in order.

 

Thanks guys - I didn't encounter the issue running the stock Checkmate 10-round mags. Will do some more testing.

I'm assuming worst case scenario I just get a Sadlak extended bolt catch. LRB built the gun so it's a mix of their parts + USGI parts.

 

I have an LRB, and that was one of the problems I had. THe bolt would not go back far enough to catch on the bolt stop. At the time I did not dare question the LRB receiver, and solved it by grinding 1/8" off the back of a USGI bolt stop. However in subsequent discussions have heard that some of the LRB receivers had a little extra material in the underside, so the bolt could not quite go fully back.

So I would suspect that is your problem: the bolt cannot go fully back. You could take a dremel to the receiver, or you could grind a little off the back of the bolt stop. While the receiver might be the source of the problem, it is much cheaper to grind on the bolt stop, so I'd start there, regardless of who caused the problem.

 

Hmm, interesting. Are you saying your rifle couldn't lock on the bolt catch at all?

 

I don't recall the exact symptoms. If I recall, the bolt catch would barely hook on the rounded edge of the bolt, but not quite rotate up into it's full hold position, so a bump, or removing the magazine would let it slip off and the bolt would close.

My solution was to grind maybe 1/16" off the back of the bolt stop, and it worked.

I know the back inside corner of the receiver is a difficult place to machine, and LRB needs to spend hand work with a Dremel to get the inside corner cleaned up, so I suspect that was the problem.

 

Got it. I noticed that the Fulton Armory 10/20 mags don't push up the follower as much as the CEI 10 round mags (maybe 1/16 of an inch lower).

Before grinding the back of your bolt stop, had you considered getting an aftermarket stop (like the Smith Enterprises one)?

 

I notice there is a tendency to blame the bolt stop. A worn bolt stop will often fail to hold the bolt open. However, the follower can also be the problem. Some magazine followers will over ride the bolt stop. When this happens, the bolt will release when removing the magazine as the follower pulls it down out of engagement. It is fairly common with after market magazines. It can also happen when the receiver/stock geometry are not quite right, resulting in a condition that pushes the magazine toward the op rod, away from the bolt stop. Sometimes the receiver will have excessive shuck in the receiver bridge area that allows the bolt to position itself so that the bolt stop will not hold. Gets complicated...