I remember reading somewhere about an 1860 Colt "Long Cylinder" 5 shot (like a Remmie) private conversion in .46 Short Rimfire. I thought it was McDowell's book, but I checked the book and can't find it. Maybe it was one of the antique firearms auction sites.
The .46 Rimfire was a perfect cartridge for the Remington New Model Army (so called "1858"). With a thin plate and a new 5 shot cylinder, no other changes had to be done, not even to the hammer. The .456" bullet of the .46 Rimfire was a much better fit for the the bores of the 1860 and 1858, than the .44 Henry with its .442" bullet. Accuracy with the .46 in the Remmies was very good. but from what I have read, the accuracy of the .44 rimfire bouncing down the barrel of the average long cylinder conversion (not 1872 Open Top) was somewhat erratic.
Any help would be appreciated.