Action not working when nut is tighten

[bwarren]

Im at my wits end. When I put the barrel back in the receiver and tighten the nut down the action just slides back and forth and the action release
will not depress. Now if I back the nut off 1/2 to 3/4 of a turn everything works as it should. Also I have noticed that when the nut is tighten as it should be it seems as if the fore end/bolt isn't going forward enough for it to lock in place but again if I loosen the nut and let the barrel slide up a sixteenth to a eighth of a inch it works like it should be I know that not right. The gun worked flawlessly for two years then I had a jam to where I barely got the action back but worked fine after I got it unjammed then about 2 boxes of shells later it jammed again and now I have this issue.
Any help would be greatly appreciated.

[Scorpion8]

Pull the barrel off and examine inside the receiver. Make sure both side rails are still in place and riveted to where they are supposed to be, or haven't slid backwards. Then carefully re-install the barrel making sure the action cut-outs align perfectly with the ejector rail slot. Tighten the barrel/magazine cap nut back down and give us a report. Any pictures of anything odd you discover would help too.

[bwarren]

Thanks Ill give it a look. I did notice last night when I was looking at it that when I tighten the cap I could tell something was moving back into
the slide lock lever causing it to become stuck.

[Scorpion8]

Thanks Ill give it a look.

Any update?