Howdy
Although private gunsmiths did convert Remington New Model Army revolvers to shoot cartridges, most were done by the Remington factory in Ilion New York, under license from Smith and Wesson, who controlled the Rollin White Patent. According to Neal and Jinks, S&W and Remington signed a contract in February of 1868 (only a few months before the White patent expired) to convert a total of 4,574 revolvers to fire cartridges. These revolvers were converted to fire a 46 caliber rimfire cartridge. I believe they were five shot revolvers, not six, because of the size of the cartridge. The work was done between September 1868 and April 1869. Most were purchased by B. Kittredge and Co. of Cincinnati, a large S&W distributor. S&W charged Kittredge $3.3625 per pistol for the conversion. S&W kept $1.00 of this amount as their fee, and paid the remaining $2.3625 per pistol to Remington.
I paid less than $150 and more than $60 for my copy of McDowell, and no I ain't saying how much. If you want detailed descriptions, as well as many, many photos of the various types of conversions, as well as terrific engineering drawings, this is the book for you. The Adler book gives a nice overview and lots of glossy color photos, I have both, but it does not compare to the McDowell book. There are four McDowell books on Amazon right now, each less than $145. The Adler book costs $45. You get what you pay for.
First off, the Colt Thuer conversion was not done by gunsmiths, they were all done by Colt, either in Hartford or London. Alexander Thuer's design was an attempt to get around the White Patent. White's patent for a 'bored through' cylinder was taken to mean a cylindrical chamber bored through the cylinder. So Thuer came up with his design which relied on a 'reverse' tapered cartridge. The chambers were bored with a taper to match the cartridge. This managed to get around the White Patent. The Thuer cartridges came in 44, two 36, and 31 calibers. The cartridges were rammed in place from the front using a modified loading lever. All that prevented the cartridges from jumping forward when struck by the firing pin was the friction generated by ramming them into the cylinder. Percussion cylinders were modified to accept the cartridges, and a conversion ring containing a spring loaded firing pin was mounted at the rear of the cylinder. The Thuer Conversions were produced from 1869 until 1872. They were not very commercially successful, only about 5,000 were made. They are extremely rare and valuable today.
Here is a photo of a typical Thuer cartridge.
View attachment 821605
The White patent was due to expire in 1869, and it was obvious sales of the Thuer conversion were not going to take off. Colt designers were working hard to come up with a successful cartridge design, and produced many prototypes. The most promising was designed by Charles B. Richards.
This is a Richards conversion based on the 1860 Army Colt. The cartridge it fired became known as the 44 Colt. This cartridge was designed to fit into the smooth chambers of the 1860 Army Cap & Ball chambers, so it used a heeled bullet.
View attachment 821606
The cylinder was cut down to remove the nipple area at the rear, and a new ratchet was formed.
View attachment 821607
A conversion ring was screwed to the frame. The ratchet portion of the cylinder fit inside the conversion ring. The conversion ring had a loading gate.
View attachment 821608
The hammer was shaved off flat at the rear and a spring loaded firing pin was mounted in the conversion ring. A rear sight was also machined onto the conversion ring.
View attachment 821609
An ejector assembly was fitted into the hole under the barrel where the loading lever had been.
View attachment 821610
The Richards conversion was produced from 1873 until 1878, coincidentally being produced at the same time the 1873 Single Action Army was being produced. About 9,000 Richards Conversions were built. Interestingly enough, many of the parts for the Richards Conversions were not converted from Cap Lock revolvers, but were made up new.
William Mason was one of the best designers at Colt, he was the principal designer of the 1873 Single Acton Army.
Mason obtained patents for improvements to the Richards design in 1872. The Richards-Mason Conversions eliminated the expensive extractor assembly of the Richards Conversion, substituting a simpler extractor screwed to the side of the barrel. The Richards-Mason Conversions had a much smaller lug under the barrel to accommodate the simpler extractor mechanism. It also did away with the conversion ring mounted firing pin, instead a firing pin was fitted to the hammer nose. Richards-Mason conversions were produced on the 1860 44 caliber sized frame, the 1851 and 1861 36 caliber sized frame firing a 38 caliber rimfire or centerfire cartridge. There were also Pocket Models converted using the Richards-Mason system.
There were about 16,000 Richards-Mason Conversion revolvers made.
The last of the Colt Conversion revolvers is simply known as the Open Top. Produced between 1871 and 1872. This model was actually not a conversion revolver per se, these were designed and built from the ground up as cartridge revolvers. They had no conversion rings, the cylinder accommodated the cartridges and filled the entire space between the barrel and recoil shield. They fired the 44 Henry Rimfire cartridge. This model was unique in that it had a small rear sight machined on top of the rear of the barrel. When the Single Action Army started being produced in 1873, Open Top production ceased with about 7,000 made.