Let's discuss percussions, particularly the "cap" in "cap and ball." There's a lot of percussion Kentuckies made as such, and many more that were originally flints and were period converted to percussion, which, to many, was seen as the normal technological upgrade of the day. But, when were those days? Let's first try to pin that down.
A man in England named Howard first identified fulminates in the year 1800. For our purposes, it suffices to say that a fulminate is a chemical compound containing an unstable, friction sensitive ion. Whack one and it will explode. Fulminate of mercury was soon seen as useful in the firearms industry.
A Scottish minister from Aberdeenshire named Alexander John Forsyth is normally credited as the person who invented the percussion cap, first encapsulating fulminate of mercury in a tiny copper cup, and using it to detonate his shotgun through a nipple attached to the barrel. He wrote that this was an invention of necessity, because he was missing birds while hunting, the consequence of the time lapse between primer ignition and charge ignition in his flintlock, along with that big puff of smoke. He was the first to see the value of fulminates in eliminating this problem. Hence in 1807 he was granted a patent for his invention. Note, most historical commentary indicates that it was not until after the lapse of this patent that the percussion system proliferated. If I am correct, that puts us beyond 1817. Incidentally, the first U.S. military rifle to employ the percussion system was the M1833 Hall. Arsenals also converted many M1819 Halls to percussion.
I think that it is safe to say that there was little or no percussion application to Kentuckies until 1820 and afterwards. Some rifle commentators have suggested 1830 as a good guess for the introduction of percussion ignition to the trade, allowing for the time lapse for technology to take hold. I find this a bit late, but can buy 1825 as a target date.
Incidentally, there was a Joshua Shaw in USA who patented a similar system in 1822, so we are just establishing the time period here, regardless of whom you wish to credit with the invention. All we are doing now is ruling out proliferation of percussions prior to 1820 as pure anachronism. All this is based on recorded facts.
Now, what happened afterwards? Here's my opinion intertwined with the facts I have. I believe that most conversions were done between 1825 and 1845. I also believe that this period saw the building of numerous flintlocks and percussions built side-by-side in the shops, based upon customer preference. Sort of like buying a car in the 1960's...the salesman asked you what you wanted...automatic transmission or "straight stick"? You ordered one or the other.
The next step was the containment of the fulminate charge as a primer in a self-contained cartridge. As you know, while the standard arm of the Civil War was a cap and ball rifle-musket, cartridge firearms were used then, too. For military purposes and mass consumption, the days of both the flint and percussion system were finished, except for traditional sportsmen and firearms enthusiasts.
The exception would be a manufacturer like Henry Leman of Lancaster, PA , who built percussions into the 1880's and refused to re-tool his factory to build cartridge arms. One of his main customers was the Bureau of Indian Affairs and, from all appearances, his products continued to be distributed to Indians well into the cartridge era as intentionally outmoded technology. Yes, there were old-timers who continued to make an occasional muzzleloader afterwards, but this was no longer the norm for firearms manufacture.
I have lived long enough to witness several times the conservatism of old age and experience when something new comes out. At Camp Perry in the old days, the oldtimers refused to give up their bolt action 1903 Springfields when the M1's replaced them. Same thing happened when the M14 came out. Some said it would never be as good as the M1. There is still room for debate on this, but scores improved as the years went on (at least until the M16 came out).
So my bet is that many hunters came into a shop like M. Fordney's in the late-flint/percussion era and ordered a flint in preference to the new system. I can hear it all now: "You can't outshoot my flint with your new-fangled percussion." "What do you do when you run out of caps?" "Prove to me that it is really faster." "I can light a fire with my flint and you can't with your cap 'n ball." Then some crack shot probably went out with his flint and won a match or two and refueled the whole issue.
So, again, we have an overlap of technology, a blend of the kinds of rifles built, and exceptions to the norms. By the way, I am not a dyed-in-the-wool advocate of reconversions. My feeling is that if a great rifle comes down to me that has been converted neatly and the gun needs nothing else, I let it alone. As a matter of fact, I see history upon history which would be destroyed with reconversion. On the other hand, if I encounter a wrecked gun that was originally flint, and it needs a lot of work, then I see it as a candidate for reconversion. That's just my take on it.