I recently purchased a winchester model 12 and noticed a very slight bit of play where the barrel goes into the receiver. I took it to a local gunsmith and they made an adjuistment on the set screw but the screw seems like it will back off with time. If anbody has any input I sure would appreciate it.

M12 has a bushing on the rear of the barrel that can be adjusted for looseness in the frame. It is held in place by a locking wedge with a screw behind it. This won't come loose. There is no set screw involved.