A little trouble with an AR. Bolt won't lock

M

Murdock

New member
I bought a used Lone Star carbine with collapsible stock as a spare back up for my primary carbine. (I'm headed to Thunder Ranch and they recommend a spare).

I replaced the cheapie collapsible stock with an A-1 stock, and used the buffer tube, recoil spring and buffer from an A-2 to do it.

The rifle functions fine except for not locking open on an empty magazine. This fails to occur after the last round is fired, and when manually opening the action.

Switching the A-2 spring and buffer for the carbine spring and buffer didn't work either. I tried the carbine buffer with the rifle spring, and vice versa. No joy.

The buffer slides freely in the tube with the spring removed. The bolt lock operates fully with any magazine I try when I take the upper off the gun.

When I hold the bolt lock in with my thumb when firing the last round, the bolt locks open normally. When I retract the bolt manually, I have to press the release lever pretty hard to lock it open, but the bolt will slam forward if I rotate the rifle 90 degrees, as when inspecting the breech.

This has got to be a simple fix, but I'm not getting anywhere.

Recommendations? I may just take it with me like it is, as it's just the spare and not my primary, but would like to get it straight if I can.

I will post this on the "smithy" too. (Should have thought of that first):eek:

Thanks.
 
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M

Maxem0815

Moderator
Try replacing the magazine, if it still does the same thing I would look into the bolt hold open catch and replace that it could be worn. But it sounds to me that more like the catch since you say if you move the gun it slams forward.
Possibly a spring behind the catch.

Mace

Happiness is a belt fed weapon with lots of ammo
 
M

Mobuck

Moderator
I've seen several new lowers that needed some breakin and lube to get the bolt hold open to work consistently. Did you try a different mag? Take a few minutes, lube the plunger and pivot, and work it 100 times or so. This might be enough to free it up. It doesn't take much of a burr or grit to prevent forcing the hold open up quick enough to catch the bolt.
 
T

Technosavant

New member
I'd start by trying different kinds of magazines- GI style, Pmag, etc. If they all don't work, then you know it isn't the mag (you didn't say you'd done this, so if you have, disregard).

Then, I'd look at the bolt hold open. I don't know that there's much reason to take the thing to a gunsmith; ARs are pretty simple creatures and it's a simple swap. But you'll want to isolate the failure- make sure it isn't the upper/bolt by swapping another upper onto the lower. If it still won't lock open, then it's definitely the lower.

You can get a new bolt hold open and install it in minutes with a hammer and punch, so if that's chipped/broken or just not formed correctly, then it's a cheap/easy fix.
 
M

Mobuck

Moderator
I just had another thought. I recently had a problem with a new rifle that would n't lock open. It turned out to be a kinked action spring that wasn't allowing the bolt to go fully to the rear part of the time. It was going far enough to eject and function but not always far enough to be caught by the lock. Replaced the original spring with a better quality from Brownells and no more problems.
 
H

HiBC

New member
Here is my hunch.You went from a A-2 stock to an A-1 stock.So,you got to leave out the spacer.The A-2 screw is the right length to go through the spacer.You might not have had an A-1 screw and used the A-2 screw,so about 5/8 of the screw is sticking where it does not belong.Maybe?
 
M

madcratebuilder

New member
A1 stock needs the A1 butt screw, shorter than the A2.

The bolt stop should only have the spring tension against it, it has to move easily.

When I hold the bolt lock in with my thumb when firing the last round, the bolt locks open normally. When I retract the bolt manually, I have to press the release lever pretty hard to lock it open, but the bolt will slam forward if I rotate the rifle 90 degrees, as when inspecting the breech.
Click to expand...

The bolt stop is binding.
 
D

Dfariswheel

New member
I have a friend who's Bushmaster started doing this after installing a stock spacer.
He looked and looked for a long screw or stock problem.

I took a look and found that the yellow plastic rear end of the buffer was coming out of the buffer.
Like many commercial AR rifles, the plastic end piece of the buffer is not pinned in place, it's only crimped by the buffer itself, and recoil was pushing the buffer end cap out by inertia.
 
M

madcratebuilder

New member
I took a look and found that the yellow plastic rear end of the buffer was coming out of the buffer.
Like many commercial AR rifles, the plastic end piece of the buffer is not pinned in place, it's only crimped by the buffer itself, and recoil was pushing the buffer end cap out by inertia.
Click to expand...

That is getting cheap, I had to go check my two BM buffers in the parts box, both pinned, most be old stuff.
 
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