Gentlemen, just got a digital caliper. The diameter of the rim is 13.3 mm or .525 inches and the thickness, breech toward the muzzle, is 2mm. The diameter of the brass looks to be around 11.8mm, I will be able to get a better reading after I get the cast made.

Looks like is a little larger than a .45 Colt, tomorrow I will check a Colt round, I know it isn't the right cal., just to see how close it fits. My book shows a Colt round , the rim, at .512 inches.

I take it that you plug the barrel then pour in the melted wax, let it cool then push it out to get a measurement? This is all new to me, I'll have to check out the you tube video.