Originally Posted by jjmitchell60
You need to take a set of calipers and measure across the inside of the muzzle to be even close to what caliber. It should be marked on it some where as to either caliber, bore, or mm. Pictures also help in identifying what type thus what caliber it should be.
I used a caliper to get the measurements I mentioned.
It is not marked anywhere.
Maybe it is a shotgun (fowling piece)? Could be about 20 ga.