Merwin Hulbert first model my Dad bought about 50 years ago for $15. Center fire probably .44 M&H cal. None of the .44s I have, will go in and a .41 is sloppy.

Looking back in this thread is a MH single action with the top strap and crude engraving. Reminds me, in '64 Mexico City I bought one with top strap, full length barrel for about $15. Sold it soon after in US for $65. On its barrel left side was the name Anitua & Charola, maybe made in Mexico. I remember comparing the lettering with the Hopkins & Allen on mine (above) and it looked pretty much the same.

Wonder what mine is worth. I'm interested in Colt 1905 .45ACP automatics mostly now.