AR-15 Bolt Hold Open Issue SOLVED!

Ganderite

Ganderite

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Location
Farm south of North Bay
New NEA 10.5" About 300 rounds fired.

Regardless of the magazine used, sometimes it locks open with 1 round still in the mag.

What can cause this? What do I need to adjust?

It took 30 seconds to diagnose the problem, after the posters below told me what to look for. There is no spring to hold the latch down. It bounces around on recoil and grabs the bolt.
 
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Wild guess here... Maybe the bolt catch or lower is not up to spec 'cause the back of the follower is what pushes the bolt catch upwards to arrest the bolt from going forward after the last round is cycled.

First verify the firearm is unloaded and safe to handle. Keep all live ammo well away from your workspace and wear safety glasses! Now that the safety disclaimer is out of the way...

If it's catching with one round in the mag all the time, load a snap cap into a mag.

With the bolt closed, fully insert the mag.

Slowly pull the bolt back using the charging handle while looking into the ejection port. You will need some good lighting.

Check and see if the bolt catch is lifting up as you pull the bolt past the snap cap. Is the arm from the catch sitting on the back edge of the follower?
 
Hmm, my first idea is that maybe the bolt stop is a bit too long on the bottom, causing it to contact the magazine follower early. Or the follower is maybe tilted/otherwise in a position to contact the bolt stop.

If it happens with a variety of magazines, that's the only thing I can think of. Unless maybe there's a burr or some debris in the hole for the bolt stop spring. All I can recommend is to give the thing an inspection, see if there are any tool marks or such that could be interfering with proper movement of the bolt stop.
 
Is it always with one round left?
Is the bolt catch lever spring in good shape? Maybe it's just bouncing while the rifle is cycling.
Sounds weird but shouldn't be too hard to track down, it's a pretty simple system.
Where are you? Maybe someone close by can take a look at it with you.
Good luck.
 
I took the latch off, expecting to see no spring. But it is there, along with what appears to be a detent pin. But it does not stand proud of the receiver to pressure the latch. I suspect a burr in the hole has captured the spring. How do i get it out? The hole is blind.
 
Ganderite said:
I took the latch off, expecting to see no spring. But it is there, along with what appears to be a detent pin. But it does not stand proud of the receiver to pressure the latch. I suspect a burr in the hole has captured the spring. How do i get it out? The hole is blind.
Click to expand...

I have had this problem; either dirt or a burr got in there and has jammed it. The million dollar question is how to get it out. You can try to bounce it out, oil and compressed air may help. But you may have to bite the bullet and get a small file or drill bit in there and make the hole a little bigger. Some people are lucky and can grab the tip of it with pliers or use some sort of prayer combined with magic to get it out. Needless to say after hours of searching for a solution there was no good one, as I had expected and you probably currently suspect.
 
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