I use PRB (patched round ball) in my flinter. Never had a problem with them in terms of killing power and accuracy. If you are talking about a round ball from a smooth bore, well then, that is an entirely different matter.
I used maxis until i ran out and had a lot of roundballs so I started using them and last year I swore that I had hit one and couldn't find blood she took off like a shot and her tail was down like she was hit I thought for sure I had hit her I heard from some that they don't bleed out right away with roundballs Idk I never shot one with the flintlock aways had a bad flinch until last year I finally got over it
My main roundball rifle is a .50 with a 30" barrel; 80-90 grains of 2f and sighted 1" high at 50 yards to be dead on at 75 and a little over 2" low at 100. Deer shot under about 60 yards go down within a 75 yards usually if the shot is true. I have chased em quite a ways if I take a shot at longer range and the shot was found to be true to aim in most cases. I tend not to shoot over 75 yards with my current roundball rifles. If I were to go with a .54 caliber it might be better but I can't say as I have never tried it.
In the past I have killed deer with Maxis,Powerbelts,and Round Ball in various calibers.
All I use now is Round Ball.Have yet to find a deer that will live with a hole in its heart or lungs if you put one there.
I have found the RB to be the most accurate,flat shooting,and economical projectile to shoot out of my flints or percussion muzzys.
PRB's are very accurate and have good killing power. I currently do not use them in my .54 because the T/C Maxi Hunters are shooting very good and are very easy to load. The PRB is a great choice!!