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Page AR-15 » Troubleshooting
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Posted: 7/23/2017 12:47:20 PM EDT
My most recent build is giving me fits.
The bolt locks shut. And I mean LOCKS.
I have to use a mallet to get it to unlock.
It locked up the first time I fired it.  It locks up when cycled with a dummy round.
I changed out the bolt with another rifle. Still locks up.
Link Posted: 7/23/2017 12:51:08 PM EDT
Did you change the bolt or bolt carrier? Have you checked your gas tube alignment and your barrel extension? Pics would help
Link Posted: 7/23/2017 1:14:32 PM EDT
Changed both the bolt and carrier.
I'll pull the gas tube assembly to rule that out.
Thanks for the ideas.
Link Posted: 7/23/2017 1:24:13 PM EDT
What brand bolt?
Is the cam pin hitting the upper receiver?

Pics of the bolt face and lugs.
Link Posted: 7/23/2017 2:30:41 PM EDT
Pics of feed ramp alignment. Can indicate a barrel extension pin which is not clocked properly.
Link Posted: 7/23/2017 4:27:28 PM EDT
Link Posted: 7/23/2017 5:15:20 PM EDT
Topic Moved
Link Posted: 7/24/2017 12:54:28 AM EDT
Link Posted: 7/25/2017 5:51:05 PM EDT
Discussion ForumsJump to Quoted PostQuote History
Insufficient headspace is a possibility.........what ammo are you using and what brand barrel?
View Quote
I imagine this is the problem. The worn bolt had plenty of clearance, the new one's headspace is too tight for your ammo.
Link Posted: 7/26/2017 12:30:52 AM EDT
You say that the action locks up when fired or when a dummy round is chambered...

Does the action lock up if the bolt is closed on an empty chamber?

The dummy round that you tried.  Did you make it from a fired round or did you use a commercial made dummy round (plastic or metal)?  Did you full length resize the casing before inserting the bullet.  A round fired from a different gun has expanded to fill the chamber of the gun it was fired in (which is not the same size as your gun).  Odds are that if a casing is not resized, it will jam when inserted into a different gun.
Link Posted: 8/20/2017 11:55:27 PM EDT
A similar problem was a small piece of brass on the forward side of the locking lug. Younger eyes and a pick solved the problem.
Link Posted: 8/22/2017 6:52:43 PM EDT
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