The frame size will not be listed in the serialization book. I am not sure what "20" you are referencing but the frame size will be on the barrel lug. If it is a 20 gauge gun it could be a "0" frame, a "1" frame or even a "2" frame. A one frame 20 gauge is uncommon and a "2" frame 20 gauge is rare.
__________________
"A man who carries a cat by the tail learns something he can learn in no other way."
|