A 44-40 pistol barrel is no longer than a muzzleloader barrel. And the 220 grain bullets used in the 44-40 aren't really any different than a 250 grain muzzleloader bullet. In the short distances, a round ball comes out faster and doesn't lose that much velocity at 30 yds anyway. Sure if yer talkin 100 yds. However, a 490 or 535 PRB packs a fair wallop and makes a big bloody hole. Or for that matter a minnie ball or modern conical. There some folks who shouldn't be permitted to hunt deer with a 30.06. Few who carry a pistol into the woods will use it as their "first shot" gun anyway. Mostly they will be back up for second shots, when and if needed.
And, I have loaded very short soft lead 45-70 bullets and 455 Webley bullets in my Ruger Old Army. With great results. The 455 wad cutters are only a half inch long and really displace little room that powder would have held in the chamber, and they weigh in around 200 grains.
It isn't always the energy of the ball or bullet. or hydroshock. A 54 caliber hole is a shock inducing wound whether 6 inches deep or pass through. In the book Treasure Island, Long John entrusted a pistol to Master Hawkins, telling him that a wee charge of powder and a large ball is the way to kill a man.
In the War of Northern Aggression, 60 grains of powder and a 577 PRB were considered by most of the world's armies as lethal on humans out to several hundred yards. Black powder Ballistics really haven't changed in 150 yrs.