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I have a very nice Colt AR. After A mag goes empty, the bolt stays towards the rear and I have a Dickens of a time getting it to slide forward again. It remains locked to the rear, and I can’t even open the rear.

Any thoughts about wat is retaining it towards the rear?

Hit your bolt release and it will go forward.

No joy. The bolt is locked too far back.

If the bolt is locked back further than the bolt release, there's something broken, or there's a piece of debris lodged in it.

Try undoing both front and rear takedown pins, and slide the upper forward and up. Try to see what's binding the bolt.

If that doesn't work, you'll need to remove the stock and unscrew the buffer tube.

You might need a gunsmith.

Good luck.

Does it cycle by hand easily? You should be able to see where it's binding. Maybe something is in the receiver extension tube...

It almost sounds like the bolt is up against the hammer. And it sounds like the hammer is not in the cocked position.

I don’t get why it would only occur after the last round in mag. Unless it has only happened once and a coincidence that debris lodged then.

I had a BCG get stuck in the tube, but it was pilot error. I had gone to change buffers and got distracted, forgetting to put in the new spring/buffer. Just lightly banged the muzzle onto the carpet and she came loose.

Uffdaphil wrote:I don’t get why it would only occur after the last round in mag. Unless it has only happened once and a coincidence that debris lodged then.

I had a BCG get stuck in the tube, but it was pilot error. I had gone to change buffers and got distracted, forgetting to put in the new spring/buffer. Just lightly banged the muzzle onto the carpet and she came loose.

That works with my rifle. A couple of good bangs and the bolt slides forward.

Uffdaphil wrote:I don’t get why it would only occur after the last round in mag. Unless it has only happened once and a coincidence that debris lodged then.

I had a BCG get stuck in the tube, but it was pilot error. I had gone to change buffers and got distracted, forgetting to put in the new spring/buffer. Just lightly banged the muzzle onto the carpet and she came loose.

That works with my rifle. A couple of good bangs and the bolt slides forward.

Is it lubed well?
Also, open it up and inspect for a blown primer or other debris.

Have you found your problem yet ? Have you tried the complete upper on a different lower, I'm thinking that the buffer tube or buffer spring detent but a different lower test would eliminate half of the guessing.

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