Milton, I would agree that looks like a 10ga. on a 2 frame(which is a nice configuration). That would have been a nice one. I have noticed in some of the early guns the breach/chamber walls are much thinner on the smaller frame guns(even though there is not a number designation for frame size).
When I bought a relative early 12ga. Lifter(#3492) I thought the same thing on the thickness of the breach/chamber walls. Here is that thread which has some good pictures:
http://parkerguns.org/forums/showthread.php?t=20301
The early guns(like all Parkers) are a lot of fun!
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