Hi all.

Looking for a bit of help on a caliber ID.

I have an old Hopkins and Allen falling block shotgun that someone put a rifle barrel on.
The caliber is not marked in any way.

I picked up some Cerrosafe and this is what I came up with:

Attachment 103535

At first I thought maybe 500 Smith and Wesson but it's too short for even that.

Any thoughts?
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