I'm guessing here(need more info for a better ID) but if the shotgun is a WesternField pump with the hump back profile of the Browning A-5 what you have is a Stevens either a 520 or a 620(that's from memory, books are in the shop). Parts are listed in the GunPart Corp book.. Repair procedures I don't have but-- gunparts corp has a website and they have some parts blow ups on line(their catalogue is a great reference) and I have their address below.. If you have problems just ask..I grew up with one of these my mother bought it for my dad when they were first married. I also bought a 20 gauge in the double hump, from a friend.. There were several variations but they are not too hard to work with..