Hi all, really need some help. ive got a black synthetic webley 810 semi 12g 3 shot, i bought it second hand with no paperwork i.e manual. it has begun to jam more often and the small tube on the end of the mag tube (the one with the metal ring around) seems very loose and the metal ring just falls off when i strip to clean (its not broken, just loose), is this normal? also read alot about "o-rings" in semis, mine doesn't have one, should it? i can see the two holes where the gases escape but no ring??? would really appreciate some pictures and maybe if someone could go to the trouble of scann