I've been doing cartridge conversions as part of my amateur(ish) gunsmithing hobby. It's a sickness that started with using Kirst Gated Conversions and progressed to boring out C&B cylinders, then lining them for smaller calibers. Recently though I got my hands on a chunk of 4340 H/H round bar and had a go at making my first cylinder for a reproduction Remington 1858, just to see if I could.
I turned it down on the lathe, then cut the sprocket for a five-shooter because the standard cylinder isn't large enough for six rounds of a .45-caliber cartridge. Then I located and cut the locking notches and timed the cylinder. With that done I line-bored the cylinder, then ran a chamber-reamer in from the other end.
I chambered it for .450 Adams, since I already reload that for some of my antiques and it's a nice, low-pressure load. I made this for a conversion I had done previously in .44 Colt (original.) Results have been good; makes for a nice, soft-shooting gun that is accurate and a pleasure to shoot. The .44 Colt conversion has moved on to a new home in another gun, BTW; waste not, want not and all that.
This opens a whole new world of possibilities- I've already turned and timed a new cylinder for a Colt 1851 reproduction, a six-shot that will be chambered for .38 S&W (I line the bore with .357 liner.) Anyway, it was a fun and interesting project and I thought I would share it.