I have an early, '66 or so, 12 gauge Winchester Model 1200 that seems to be coming out of lock up after a shot is fired. Lately upon firing a shot I'm surprised to find the fore end bottomed out in the retracted position seemingly with little to no help on my part. I have the twin gun in 20 gauge that doesn't do that. The only parts I can think of that are involved with lock up are the breech bolt and the barrel. I have tried different barrels and still have the issue. Am I correct in assuming the problem is a worn breech bolt? I've stopped shooting it till I get it figured out and fixed. Any other possibilities?