There is another factor with heavy recoil and reduced velocity or for that matter with almost any firearm. If you fail to shoulder/cheek the rifle consistently you will have fliers. The heavier the recoil and the longer the barrel time the worse this may be. With some BP arms I own it can be surprisingly large at extended ranges.
Velocity: Its the key to trajectory. RBs have dismal ballistic coefficients but high, for BP velocity potential. Short/light for caliber conicals/cylindricals are little better. Which means they don’t shoot as flat since its hard to get the velocity as high. A 50-54 caliber round ball driven at 1800 fps/1900 fps will shoot flat enough for a center hold on a deer from muzzle to about 120 yards. IF its sighted for best trajectory. Which means about 1” high at 100. ANd many modern ballistics apps/programs seem to get a little wonky when the BC starts with a .0. But its possible to test this at the range. In explanation, pardon me if you know this already. A deer is going have a broadside kill zone 6-8 inches high. SO the ball should not be more than 3.5/4” high or low for a “point blank” range. Point blank being no offset hold for trajectory needed. Past 120 yards the ball has lost enough velocity that its falling pretty fast. So shooting past 120 yards on game is not good. Unless you are VERY confidant on you skill and the rifle and you KNOW THE RANGE. Where I live out in the big open with nothing but grass this can cause real issues. Depending on the light on the animal it can cause a 140-150 yard shot to look like 100. So after and irritating incident with a mule deer buck I, which I paced off after he left. He was embarrassingly farther out than I had eye ball ranged, I bought a good 1000 yard or a little more range finder.
For hunting you need basically three things, sufficient velocity for a long “point blank”, sufficient accuracy to assure the spot aimed for is hit and finally adequate penetration. With the sighting generally used, the long lock time (flintlocks are extreme in this case, no millisecond lock times here) and the trajectory shooting much past 100 yards can be risky. So the one advantage of the elongated bullet, penetration at greater distances, is pretty well negated anyway. Unless you have a range finder and a sight like you would find on a long range ML target rifle. These things were all pretty well known by 1860. But humans continue to ignore history or have simply not thought about or studied it and not just in firearms usage. Failing to do this or have enough experience in some cases, result in mistakes from long ago being repeated with the same result. And I have shot a number of animals up to Buffalo with elongated bullets. For example, a soft alloy 500 gr PP 45 cal will almost shoot through a buffalo bull end to end. A soft 400 gr 44 will cut off a limb(s) in a pine tree, hit the deer tumbling end for end and still make 18-20” of penetration and almost exit at the front (it had been wounded by a hunting companion. I have shot critters with about every projectile type imaginable and one you would not think of. They all work fine. The RB is a very good hunting projectile so long as its properly sized for the game at hand. Shooting Elk with a .315 RB probably not a good idea unless its close range head shot from the side. Nope never did that.
Then there is the “jump the string” thing the bow hunter talk about. I was watching a video featuring a guy that was a PhD that had studied deer basically his entire career and taught it in college till he retired. He was talking about their color vision, never wear white or blue, its bad. AND how they can run through thick woods etc full speed and not hit things. Besides having the ability to see everything except about a 60 degree arch behind their head. They have about 4 times the processing speed for movement as a human. So things to them move in what would be slow motion to us. As a result I have had at least 2 deer react to the pan smoke on my flintlock causing and “off” shot (high) and in one case no deer. He thinks that the deer that jump the string with bow hunters actually react to the MOVEMENT of the arrow/bow. This for some reason appeared on youtube as I was watching it on my TV. I think its a “Deer IQ” series. Should have subscribed I guess.