Thanks!

After slugging the bore, it appears it is not a .44 caliber for sure! It slugged at .411" and I decided to try one of my sized and loaded rounds from my .40-63/70 Rigby Ballard in the chamber. It dropped right in, so might be that caliber.
Will need to do a chamber cast to ensure it is the .40-63/70, but if it is I've already got everything needed to load and shoot it! Even ammo loaded with the correct size bullet since my Rigby is the same bore size!