If your shotgun has a removable hinge pin (will have a "toggle head" and turn 1/2 turn to pull out) it is a Model 1900. But with the A prefix it is most likely a Model 1908 - which will disassemble by pulling the forestock off. There is, currently, no serial number to production date info available, although it is being worked on. Numrich/GPC (at www.e-gunparts.com
) has replacement parts for both models - but you will need to contact them by e-mail (on the home page) or by phone to confirm. Good luck!