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Posted: 1/20/2014 5:19:05 PM EDT
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Hello,
I did a build using a PSA parts kit and milled out an 80% receiver. Everything seems to be going smoothly (trigger assy went in smoothly, function checks before attaching to upper half went well, etc.). When I attach my lower to my upper and lock the bolt back it does not advance. I hit the bolt release and it does nothing. When I had my upper attached to a factory built AR lower it cycled properly. Any ideas on how to start troubleshooting this issue? 
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| It could be the bolt lock catch being tight in the milled slot on the top of the lower receiver. In order to remove the upper you will need to get the latch down. Look up through the magwell with a flashlight. With hook type tool get hold of the little tang that would ride on the magazine follower and pull it down. That should release the bolt carrier. You may need to hold the bolt back in order to move the catch. Maybe with pressure on the bolt catch pad while you pull it down as well. Once you have it off, check to see that the bolt latch is free in the slot. |
| Most of what would cause that issue, was probably already machined in the 80 percent. I am assuming that all you did was drill the selector, and mill out the fire control pocket. If the buffer detent is not centered, or the receiver extension threaded area is not the correct distance from the top surface of lower, then that can cause the carrier to bind up and not travel freely. If the hammer and trigger holes are too high, I suppose the hammer could bind on the bottom of the carrier as well. Just a few things to look at.Craig |
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Does the bolt catch release but the BCG stays locked back?
You should be able to remove the upper by pulling both pins and lifting up on the front of the upper receiver. Usually if the bolt catch is stuck the BCG will slam forward once over the bolt catch. If not you can gently pull forward. Be extremely careful doing this you do not want to get hurt or damage your rifle. I need to ask, are you sure you put in the buffer and buffer spring? |
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Quoted:
Does the bolt catch release but the BCG stays locked back? You should be able to remove the upper by pulling both pins and lifting up on the front of the upper receiver. Usually if the bolt catch is stuck the BCG will slam forward once over the bolt catch. If not you can gently pull forward. Be extremely careful doing this you do not want to get hurt or damage your rifle. I need to ask, are you sure you put in the buffer and buffer spring? No I did not put in the buffer nor the spring. 
I will attempt to get the rilfe apart and then continue. Thanks All! |
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Quoted:
No I did not put in the buffer nor the spring.
I will attempt to get the rilfe apart and then continue. Thanks All! Quoted:
Quoted:
Does the bolt catch release but the BCG stays locked back? You should be able to remove the upper by pulling both pins and lifting up on the front of the upper receiver. Usually if the bolt catch is stuck the BCG will slam forward once over the bolt catch. If not you can gently pull forward. Be extremely careful doing this you do not want to get hurt or damage your rifle. I need to ask, are you sure you put in the buffer and buffer spring? No I did not put in the buffer nor the spring.
I will attempt to get the rilfe apart and then continue. Thanks All! That would do it... 
Bounce the muzzle on a wood block on the floor a few times and the carrier should fall forwards. |
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Quoted:
I'm no Expert. But could you unscrew the buffer tube off to access the BCG and push it back in? Just be-careful wit the takedown spring, detent, Buffer retainer spring and retainer flying off. Certainly, but you might end up binding it all up with the buffer retainer and spring id you're not careful |
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Quoted:
Certainly, but you might end up binding it all up with the buffer retainer and spring id you're not careful Quoted:
Quoted:
I'm no Expert. But could you unscrew the buffer tube off to access the BCG and push it back in? Just be-careful wit the takedown spring, detent, Buffer retainer spring and retainer flying off. Certainly, but you might end up binding it all up with the buffer retainer and spring id you're not careful If the buffer and spring are not installed, is the buffer detent and spring installed? If the buffer isn't in, the retainer spring would just fall out. |
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Quoted:
If the buffer and spring are not installed, is the buffer detent and spring installed? If the buffer isn't in, the retainer spring would just fall out. Quoted:
Quoted:
Quoted:
I'm no Expert. But could you unscrew the buffer tube off to access the BCG and push it back in? Just be-careful wit the takedown spring, detent, Buffer retainer spring and retainer flying off. Certainly, but you might end up binding it all up with the buffer retainer and spring id you're not careful If the buffer and spring are not installed, is the buffer detent and spring installed? If the buffer isn't in, the retainer spring would just fall out. The buffer tube retains the buffer retainer and spring, not the buffer itself. |
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Quoted:
The buffer tube retains the buffer retainer and spring, not the buffer itself. Quoted:
Quoted:
Quoted:
Quoted:
I'm no Expert. But could you unscrew the buffer tube off to access the BCG and push it back in? Just be-careful wit the takedown spring, detent, Buffer retainer spring and retainer flying off. Certainly, but you might end up binding it all up with the buffer retainer and spring id you're not careful If the buffer and spring are not installed, is the buffer detent and spring installed? If the buffer isn't in, the retainer spring would just fall out. The buffer tube retains the buffer retainer and spring, not the buffer itself. DUH, I knew that for some reason my mind was thinking buffer tube. Sorry bout that stupid moment. Thanks for setting me straight. |
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Guys, I really feel silly. It was the buffer tube/spring. Everything cycles normally now. Going to hit the range my day off and will post an update.
Thanks all for all the suggestions and tips. 
This does cycle much lower than my other rifle. It is a sabre defense upper, fulton armory lower, don't know the trigger group, but it does feel smoother than my recent build. Looking forward to giving a range report. 
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