Pull all the way back on the charging handle, and see where the face of the bolt stops against the back edge of the ejection port.  Hence face of the bolt should stop about 1/8" to 1/4" in front of the back edge of the ejection port window.  

If the bolt is stopping too far forward (or the last 1/2" pull of the charging handle gets much harder than the middle of the pull), then suspect that the either the buffer or recoil spring is the wrong unit of the receiver extension in play, or could be that the receiver extension was not correctly milled and the void in it not deep enough instead. Hence here, tell us what type of stock and who's parts are in play.



Or could be that when the bolt catch was installed, the spring channel was not cleaned up with blasting materal still in the bottom of the spring channel, and now the spring is coil binding up before the catch be fully raised instead.  A quick check here, just shotgun the upper open, install a empty mag, and make sure that the empty mag follower is raising the bolt catch all the way itself instead.

To add, if you want to lock the bolt back without a empty mag in the rifle to raise the mag catch, then you need to pull the bolt catch top lever outwards.

If you need to see this, shotgun the rifle open install a empty mag, and as the catch is raised via the mag follower via the mag spring, and will see the postion of the lever.

Also, the think of the bolt catch as a empty mag last round fired lock the bolt back device instead.  Hence the empty mag will raise the bolt catch after the last round has been fired, and it takes the empty mag in the rifle as the rifle is firing the last round out of the mag to push the catch up in the first place.

A quick check to make sure that the buffer and spring are the correct lenght for odd ball set ups, is to pull the charging handle all the way back and make sure that the face of the bolt stops about 1/8" to 1/4" in front of the back of ejection port window edge.

If the face of the bolt does retract back past the back edge of the ejection port window, then shim the back of the extension tube void with a shim to get the face of the bolt to stop the correct distance in front of the back edge of the window (so the back of the key does not crash into the lower receviever and crack it.   Hence quarters will work as a temp fix to get the needed shim height, and then you can come up with a better shim later.

Regarding the buffer spring, easy way to make sure that is not too long, when pulling back on the charging handle with the shim in place, should not feel the spring coil bind up instead.


As for the ace stocks with rifle receiver extension, most of the time the problem is that the longer A-2 butt stock bolt needed for the tube extender, is not replaced with a A-1 shorter butt stock bolt instead (A-1 stock does not use the 3/4" end of tube spacer).  Hence with the longer bolt and the spacer not used, then the end of the bolt protrudes into the void of the tube, while caused the buffer to be limited by it, instead of the actual bottom of the tube instead.