Have a Riverside Arms Co single shotgun do not know if 12 gauge or 16 gauge that belong to my Dad Found the number RP757 stamped on rifle behind the trigger Does this tell info about the rifle?
Sorry- that is a serial number, and conveys no information. If
the barrel is not marked, you need to take it to a gunsmith who
will measure the chamber- not only for gauge, but for the correct
shell length. Just because an unfired shell fits does not mean it
is the correct shell. And it is not a rifle, but a shotgun.