I had a PM from one of our members suggesting I should make a brief write-up about accuracy and potential of these rifles.
While not the world's greatest expert, I have been shooting flintlocks for about 30 years and a hobbyist builder for about 20 years.
Accuracy potential:
Shooting from a bench, a run of the mill flintlock hunting rifle like the one I've posted here will give between 1/2" and 1" groups at 50 yards. Eyesight is the limiting factor. If one were to put a scope or high grade target sights, at 50 and 100 yards, a flintlock target rifle will give a modern center fire rifle a run for its money.
Looking sporter flintlock hunting rifle vs. sporter center fire bolt action rifle, at under 100 yards, accuracy potential is pretty much equal. If shooting offhand, there's not much difference at all.
At 100 yards; however, wind drift and drop with a round ball starts to take a toll. 100 yard groups will range between 1" and 5" with 3" being a good average. Eyesight and open "V" sights are a limiting factor. If one looks at these groups and compares with, oh, let's say a Marlin 336 with similar buckhorn sights, you're going to see about the same kind of groups. Said differently, "minute of deer" accuracy is well within reach of any shooter with even moderate skill shooting a rifle.
OK, you may ask about killing power. Ballistics tables, feet per second, kinetic energy charts don't really tell the tale here. From muzzle to about 100 yards, a .50cal or .54 cal roundball shooting flintlock is about as effective as a 30-30. In fact, most of the deer I've shot or seen shot with a .54 or .58 round ball (my favorite is these 2 calibres) drop like they were hit by the hammer of Thor. Really anything .45 up to about .58 is potent deer medicine. Over .58 in a rifle or .62 (most common caliber smooth bore) and you're getting into diminishing returns. More recoil more lead more powder for very little improved terminal performance.
.40 muzzleloaders are an interesting breed. Every .40 (and .54 for that matter) I've ever shot has been tremendously accurate. The .40 is a good small game / medium game caliber (squirrels, coyotes, fox, coon, etc.) and I know guys who hunt deer with them and say they drop fast. Below .40 and you're getting into squirrel rifle. Yes, lots of deer were killed in the old days with .38 or so rifles but I prefer to hit them with something bigger.
The stories we read about Daniel Boone and the guys "barking" squirrels by hitting the branch right below the squirrels head thus killing it with the bark are probably true. The question I have is did old Daniel just shoot low?
Probably more than you all wanted to hear.
Jeff