After building 3 AR-15's I decided I wanted to try and build other firearms,therefore, I assembled a semi m11 parts kit (MAC, Cobray, Ingram, you guys know what I'm talking about) from RPB on a Nighthawk lower receiver. Everything fit great except the hole for the barrel retaining roll pin was not drilled. I stopped there and have never fired the gun b/c the barrel was not locked in. Well this weekend I purchased a Cobray carbine. I layed the two uppers side by side, put in the pin and marked the location of the retainer hole. Then I drilled it.....Everything looked great. I screwed in the barrel. Started the roll pin. Using my roll pin punch I started tapping it home, but it would only go about 1/3 of the way. I backed the pin out from the other side and looked through the hole. Too much of the barrel threads was showing! Then I tried to unscrew the barrel and it won't come out. I guess I damaged the threads trying to tap the roll pin in place. How do I get the barrel out? Can it be fixed? What to do? Any help would be greatly appreciated!