If it's not locking up and the bolt rotates all the way closed with the trigger group out then you have only one thing left to look at. With the trigger group out it will come back quick and easy. The recoil lug on the barrel is held tight to the receiver by the post the slide rides on so unless you get that down tight with no gunk between it and the receiver you cannot expect the gun to shoot well. It is likely brittle and will break when you pop it out of the groove it slides in. If you have to remove the bolt be prepared to order another dust cover if the one in the gun is plastic. Reassemble and tighten the post the same way you loosened it. The barrel will now pull forward and with a twist it will come out from between the slide rails.Ĭlean the lugs and barrel shank now. Put it through the holes and tap with a plastic hammer to loosen, then unscrew it. Find a phillips screwdriver or punch that exactly fits the holes in the post the slide is on. Do not remove the bolt and slide just yet. To pull the barrel you need to unscrew the end of the forearm and bump the forearm until it releases from the slide. If it's really bad and a thorough flushing with WD-40 does not fix it you need to pull the barrel. Spray that beast out with WD-40, taking special care to get up around the barrel shank particularly well. Push forward on the trigger group and lift the back. Push out the two pins that hold the trigger group in place. If you can see crud in the receiver, and particularly in the bolt lugs when you open it that is almost certainly your problem.
The first most likely and easiest to deal with problem is just that it's dirty.