I have a model 500c 20 ga. that my father purchased in the early to mid 60's. It has a 24" barrel with a
C-Lect Choke. Chambered for 2&3/4" & 3" shells. It has an upside down (P) on the right side of the barrel,close to the breech. Here's my problem: WHERE IS THE SERIAL NUMBER??? This firearm...