You can get more velocity at the Muzzle using more powder, but the issue is can you get better accuracy, that is consistent? Anyone can get a 3 shot group that pops your eyes out, but can the load and gun and shooter consistently shoot that same small group with those higher powder charges?
If you don't know the Ballistics Coefficient of Round Balls, or how much this causes any Round ball to loose velocity after it leaves the muzzle, then all this gets a lot more confusing. Do you know the speed of sound? With large caliber guns, the loads given are purposely designed to keep the ball traveling at UNDER the speed of sound. The same thing goes with Shot Loads for smoothbores. With the medium calibers, such as are used for hunting deer, many hunters try to get a high enough velocity at the muzzle to keep the ball going ABOVE the Speed of Sound out to where the ball is going to strike the deer at the maximum chosen hunting range. But, short barreled guns rarely get a ball going fast enough to keep it above the speed of sound much past 50 yds.
There is also the Transonic zone to consider, and that is a window from about 1250 fps. down to 1100 fps, where air pushing against a round ball does all kinds of nasty and unpredictable- much less controllable-- things to its flight path. All these things destroy accurate placement of RBs. And, you can't do anything about them.
The more powder you put in the barrel, the more recoil you will feel, and we know that affects group size. It also delivers various shock waves in front of the muzzle, which push against the back of the ball, and surrounding air, which then has to come back to fill in the vacuum these waves create. That process disturbs the drag "cone" immediately behind the ball, affecting flight characteristics of the ball. If the crown on your muzzle is Not perfectly concentric, whatever imperfection will be magnified by the higher pressure created by the greater powder charge, as the gases escape out the muzzle around the PRB.
The current " experts" in this sport on how to get maximum accuracy from a PRB have to be the Chunk Gun shooters. They are shooting rifles off a rest, from a prone position, at an "X" target mounted out at 60 yards. The goal is to get the center of the ball as close to the center of the "X" as possible, for each of 10 consecutive shots.
The winner of this Year's Sgt. York Memorial Chunk Gun Match had a "string" that was only 4.65" long. They all shoot LONG BARRELS to achieve this kind of accuracy, Not short barrels. And, because the target is only 60 yards away, if they shoot a .45 or smaller bore rifle, they can get the ball going fast enough that it stays above the Transonic zone at that distance, and is still accurate( obviously).
100 yds. is a lot further distance, and few of even these guns can keep a ball going fast enough out at 100 yds. to stay above the transonic zone.
Short barreled guns have their place. The barrels today on commercial guns, like the T/C, or Lyman products can certainly withstand the larger powder charges. But, most deer are shot well within 50 yards, so a hunter is not particularly handicapped if he uses that short barrel MLer, and a 65 grain powder charge. A .50 caliber ball will completely penetrate ( both sides) of a deer's chest, if its shot broadside with such a load, at 50 yds. or less. If you are accurate enough in how you aim the gun, and can put that ball in the lungs/heart area of the deer, you will "make meat".
Do your own accuracy testing. Do your own penetration testing. I found, to my surprise that when I fired my .50 caliber using 60 grains of FFFg powder, and then 100 grains of FFFg powder, the lead ball penetrated the same distance with both loads. Since the heavier charge was throwing unburned powder on the ground in front of my muzzle, I backed my hunting load back, by doing accuracy testing, to 75 grains. My first deer was shot with that gun at about 40 yards, with a 65 grain charge of FFFg powder. The ball broke a rib going in, penetrated both lungs, and some major arteries above the heart, and then broke a second rib going out. The hole in the second rib was about 3 times the size of the entry hole. She staggered down a steep ravine for about 75 feet before collapsing at the bottom, leaving clear tracks, and a double blood trail along the way.
