Last year I picked up and Armi San Marcos Walker Reproduction, and over the winter converted it to fire metallic cartridges. I bobbed the barrel at 3-1/2", bored through the chambers, then turned down the back of the cylinder on the lathe. I made a breech-plate with a pass-through for loading and unloading, with a rebounding firing pin. A number of people have done conversions on these to various .45-caliber cartridges- .45 BPM, .45 Brimstone, .45 Walker etc. but of course I can't do anything normal, so I went with heel-base bullet in a .44 Caliber cartridge. I'm calling it .44-50 Walker, as the case holds approximately 50 grains of black powder. I'm using a .452 heel-base 200gr. SWC over 10gr. of Trail Boss (the starting load based on TB's instructions on developing loads.) It hasn't blown the gun up yet, so I guess they know what they are talking about. The cartridge is based on .303 British cut to 1-11/16", then carefully expanded to the proper diameter. I used large rifle primers and large pistol primers in testing- the main difference seems to be the rifle primers often take a second strike. No more rifle primers then. I don't have a chronograph so I don't know the velocity, but they sound supersonic to me. I could be wrong; we'll find out at some point. Recoil is noticeable but not bad; even in trimmed-down form the gun weighs 3-1/2 pounds so that soaks up a lot of it. It is loud- but the fireball appears smaller than expected. In better weather I'll photograph some black powder loads- that should be epic! Here's two of the .44-50 Walker rounds with a .45 Colt for comparison: Pretty happy with how this project is working out so far. At the very least I am having a lot of fun.