I have an American Frontier Firearms 1860 "conversion" like FCK mentioned above, but it appears that Dave just tapered the rebate from about 1/4 or so inches from the rear of the cylinder forward in order to emulate a rebate. There is no step in the frame. I was told this pistol was a "prototype" and very few were made. It's in 44 Colt.
I also understand that ASM did just started making pistols out of the parts they were making for Dave, hence the ASM line. The quality of the bluing and the final fit and finish on the ASM versions I own do not hold a candle to the two AFF pistols (an 1860 in 44 and an 1871 in 44).
Bishop Creek,
Your 1851 appears to have a blued frame, am I correct?
I'd also like to know what the serial number is, mine are both pretty low numbers if memory serves me.
Thanks, HH