Hi I just picked up A Stevens Model 311 Series H 12 gauge 26" barrel Serial # A755xxx When I broke it open A small U piece of steel flew out and landed on floor it fits back in and gun locks up but is it suppose to just lay on the pivot or is it broke. sorry don't know the proper names of these parts yet. Also any help on the date would be great I cant find any combination of letter and number in a oval but a lot of single marks G, Y, d in circle, SP in oval also on top of barrel there is a 5 on one side and 15 on the other does that have anything to do with the choke? Thanks for your help I really like this shotgun it looks great and should shoot just fine.