AR15 Bolt Closing when it ain't suppossed to

MEGARMS · Nov 29, 2015

Like the title says, my bolt is closing when it is not supposed to. The bolt stays open after the final round in the magazine is fired, however when I slam another loaded magazine in the gun, the blot closes without the bolt catch being pressed.

Any ideas how to fix this? Maybe just replace the bolt catch?

Mdeng · Nov 29, 2015

Don't"SLAM" the magazine in so hard you big brute!

Seriously though, most semi autos will drop the bolt if the magazine is inserted with enough force.

tomgreco · Nov 29, 2015

Does this happen with different mags?

MEGARMS · Nov 29, 2015

Mdeng said:
Don't"SLAM" the magazine in so hard you big brute!

Seriously though, most semi autos will drop the bolt if the magazine is inserted with enough force.

I have noticed this on a few of my handguns, but did not think it was normal on the rifle. Maybe I have nothing to fix?

jimbobborg · Nov 29, 2015

It's a feature, not a bug.

Mdeng · Nov 29, 2015

MEGARMS said:
I have noticed this on a few of my handguns, but did not think it was normal on the rifle. Maybe I have nothing to fix?

How hard are you hitting them?

MEGARMS · Nov 29, 2015

Mdeng said:
How hard are you hitting them?

Too hard, apparently.

Boss94 · Nov 29, 2015

Sounds like it .

outrider58 · Nov 29, 2015

You thought ''MEGARMS'' referred to what he keeps in his safe. :lol:

dist1646 · Nov 29, 2015

Sounds like the bolt catch isn't coming up far enough to engage properly. Clean, check for wear, check to insure it comes up fully. If all that is o.k., try a different bolt catch spring.

MEGARMS · Nov 29, 2015

dist1646 said:
Sounds like the bolt catch isn't coming up far enough to engage properly. Clean, check for wear, check to insure it comes up fully. If all that is o.k., try a different bolt catch spring.

I just went and inspected the bolt catch. It is clean, no signs of wear, and it does come all the way up. It is coming up far enough to catch with an empty magazine inserted and when I manually depress it with no magazine.

It is only when inserting a loaded magazine with the bolt catch already engaged (bolt open) that for some reason the bolt catch must slide down just far enough to release the bolt. Correct me if I am wrong, but it seems to me that maybe the spring I have is too strong, thereby periodically causing the bolt catch to slide down off of the bolt when inserting a mag?

I will try swapping the whole thing out and putting one in from another gun to see if that changes anything.

Magnumite · Nov 29, 2015

Is the top cartridge in the magazine striking the hold open lug of the bolt catch? If so, shorten the lug just enough to clear the cartridge.

grb · Nov 29, 2015

Geez, you animal...too strong for your own good there?

clandestine · Nov 29, 2015

This isnt really a problem in general, but its possible that it may be the result of something being wrong.

Who assembled the lower?

Can you take a picture of the bolt catch holding the bolt back (viewing through the ejection port)?

Does the Bolt Catch have spring tension when you remove the lower from the upper, or does it flop around?

Here's a neat trick I share with my students.

To test the Bolt Catch Spring, separate the upper and lower.

Lay the Lower on a solid surface and take the COMPLETE Bolt Carrier Group from the Upper and do this. Gently rest the edge of the tail against the bottom of the Bolt Catch and balance it with your finger WITHOUT adding any weight.

If the Bolt Catch does not drop or move the spring is good. If it collapses, its worn, too short, or the wrong spring.

MEGARMS · Nov 29, 2015

Thank you everyone.

I think I have diagnosed the problem and the only way to fix it is to swap this lower with the one on my dedicated .22. I am afraid that it is not the bolt catch or the spring, but rather the lower(s) itself.

I got a bunch of billet 80% lowers back in 2013 in two different styles. I spent some time today swapping lowers, BCGs, and bolt catches from various rifles. I was only able to duplicate the problem with the style "A" lower. It didn't matter which BCG, upper, or bolt catch was installed; I was always able to duplicate the issue with that style lower. I was unable to duplicate the issue with the style "B" lower, no matter what configuration of BCG, Upper, or bolt catch.

So, I will just put the style "A" lowers on my dedicated .22 uppers. Those uppers do not really make use of the bolt catch anyway.

Again, thanks for everyone's input.

clandestine · Nov 29, 2015

MEGARMS said:
Thank you everyone.

I think I have diagnosed the problem and the only way to fix it is to swap this lower with the one on my dedicated .22. I am afraid that it is not the bolt catch or the spring, but rather the lower(s) itself.

I got a bunch of billet 80% lowers back in 2013 in two different styles. I spent some time today swapping lowers, BCGs, and bolt catches from various rifles. I was only able to duplicate the problem with the style "A" lower. It didn't matter which BCG, upper, or bolt catch was installed; I was always able to duplicate the issue with that style lower. I was unable to duplicate the issue with the style "B" lower, no matter what configuration of BCG, Upper, or bolt catch.

So, I will just put the style "A" lowers on my dedicated .22 uppers. Those uppers do not really make use of the bolt catch anyway.

Again, thanks for everyone's input.

Its one of the other reasons I don't like Billet Lowers, the "standards" are all over the place. Its was just more common with Billet Lowers than Forged Lowers. Often the Bolt Catch Pocket is cut too wide or too deep, in the wrong spot, and the Plunger Bore is drilled too deep.

The main reason is they are softer, and they can peen around the Bolt Catch recess, and the Pivot/Takedown & FCG Bores wear faster.

Magnumite · Nov 29, 2015

Post #14, thanks for the check method.

AR15 Bolt Closing when it ain't suppossed to

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