I don't know, except maybe they're trying to do what all the different designers were doing back then..."building a better mousetrap?" Trying to improve on a proven product? I think that we as shooters do the same thing, trying to improve our weapons and ammo as well as techniques, only to find that in most cases that the old tried and true ways are the best.
I don't have any of the molds, but the newer design wadcutter and semi-wadcutter "minies" have been popular for target shooting with lighter charges. I have to say that they make scoring easier due to punching a neater hole in the paper. I have an old Lee aluminum mold for the 505 gr. Minie and those bullets probably were the best for my Richmond, but that mold is so badly worn and has been re-worked so many times, I have way more rejects than good rounds. I turned a new baseplug for my Lyman that reduced its weight from 485 to 420 grs. with a thinner skirt for light charges, but have found that I'm better off with the original baseplug. I guess things haven't changed. We think we can make it better. In my case, on a rare occasion I can do something that's an improvement for me, such as jag designs. But usually my brainstorms end up as a soiled note tossed in the trash or a corner of a toolbox.
I've noticed in many of the threads we've had concerning improving ballistics on the rifle-musket and the expanding ball, some shooters have asked how they can get blistering velocities, flat trajectories and massive terminal impact. The answer is: We can't. We have to realize the original use of these guns and their limitations. They are superb killing machines...against men. They will kill deer and other large game, I've done it myself. But with this rifle's low velocity, a deer can move enough when the trigger is pulled to only be wounded or missed entirely by a shooter only a little more than 100 yds. away. They're designed for use against troops in line of battle although they are great for individual targets. Soldiers in this situation cannot duck or dodge or spook when they see the smoke. (Although I have read somewhere that a battleline was spared heavy casualties because they marched into a swale just as the other side fired a volley. The balls passed just over their heads.) We can speed up the bullet by using a lighter weight bullet and using more and finer powder, but that's about it. Raise the velocity too much and the bullet is guaranteed to strip through the rifling and at the same time get a deformed or partially melted skirt. Either way you get a keyhole.
I don't know. I believe the rifle-muskets of the Civil War were the peak of the minie rifle design. The British War Department wanted a rifle that would outrange the P-53 and engaged Joseph Whitworth to come up with something. They stipulated that the bullet weight and the powder charge had to be the same as that used in the service rifle (P-53). This weapon we all have come to know and love as the .451 Whitworth. So, in order to improve the muzzleloading rifle-musket, it had to re-designed as a smallbore rifle using a much longer bullet and a rate of twist almost 4 times as fast.
As far as accuracy, sure we can improve them some by tweaking the loads and changing sights, but I don't think there's much can be done to speed them up. Nor do I want to, myself.
Sorry this was so long tg. You oughta know by now how windy I can be. :grin: