I saw something online recently that claimed that it took upwards 40 man hours to perform some of these conversion, and that making a new gun from scratch was actually cheaper.
I think that statement would need to be taken with a grain of salt. Making revolvers was not like making flintlock rifles. They were not made one at a time by craftsmen. Ever since Sam Colt perfected his mass production techniques for making revolvers, they were always mass produced. Making a revolver from scratch the old fashioned way, one at a time, would have been hideously expensive. Putting 40 man hours into an old, obsolete percussion revolver may have been expensive, but it would have been cheaper than making one from scratch.
This also has to be looked at from a historical perspective. For most of the percussion period, from 1857 until about 1869 Smith and Wesson controlled the Rollin White patent for making revolvers with bored through cylinders that could be loaded with cartridges from the rear. This took in a great deal of the percussion period with revolvers. Colt tried to get around the White patent with the Thuer conversion, utilizing a reverse tapered cartridge. While it got around the White patent, it was not financially successful.
I can never keep straight just which of the Colt conversions were 'retrofitted' percussion guns, and which were made up using existing parts, and which were designed from the ground up to be cartridge guns. This was also caused by the White patent. Although the patent expired in 1869, Colt did not have the Single Action Army ready for the Army until 1873. The conversion units were just ways for Colt to put a cartridge revolver on the market between 1869 and 1873, until the SAA was ready. The same with the Remington conversions I mentioned earlier. These were done earlier with patent royalties going directly to S&W.
Clearly, it would not have been financially feasible to convert any of these revolvers in a factory if 40 man hours had to be dumped into each gun. Mass production probably allowed them to be converted much more quickly. However many C&B revolvers were converted one at a time by individual gunsmiths. Individual gunsmiths probably could get away with sneaking around the White patent as long as they kept a low profile. S&W was vigilant about prosecuting patent violators, but they couldn't find every gunsmith in every small hamlet. I can well imagine it might take 40 hours to make parts from scratch and modify the guns one at a time. By the end of the Civil War surplus percussion revolvers were a glut on the market and could be had very cheap. Perhaps the economics worked out to pay a gunsmith to modify a C&B gun if it could be had cheap enough in the first place.
