The PRB doesn't have a bad rep in my book. More powder won't improve accuracy in a 1X48 or faster twist because there is a point where the bullet's RPM causes the ball to become unstable due to centrifical force. The structural integrity of the soft lead ball is exceeded, and it's becoming like clay--flattening out.
I did a bunch of research on this subject, as I was trying to develop a good, effective black powder deer rifle.
My first experience was with a 1X33 twist .58 cal military replica--poor PRB accuracy with 70 grains black powder. So poor I never even tried any more. I later found that 45-50 gr was what the target shooters were shooting in the military .58.
Second attempt was with a .50 cal TC Hawken; good accuracy with 65 gr but that was max before the groups began to widen up. Couldn't even keep it on the paper with 75 + grains.
Third, was the TC MaxiBall 370 gr conical. To get a flat trajectory I worked up to 110 grains black powder. That load sailed through a deer like I shot the bullet through a card board box. The 110 grain load was far to much for that light rifle, and I broke the stock at the patent breach plug. Kicked!
I read Greener's book "The Gun" and began to pick up an appreciation for the round ball. At the height of the black powder era, 1880's, the British hunters were using the 8 gauge double as a dangerous game gun. They started with a round ball, then went to the conical bullets--then were going back to the round ball because the conical "shook" the gun, damaged the stocks, etc without much benefit. The RB penetrated just as well as the conical.
So, I concluded that the round ball shooter was what I wanted for a deer rifle.
My present rifle is a 1X66 twist .53 that I shoot with 110 grains of black powder, .525 ball and .015 patch. Accurate, and to 100 shoots flat as a bowstring. I've shot a number of deer with that rifle, all good one shot kills, all full body penetration and a good exit hole that bleeds. I shot a wounded doe in the side of the head to stop it for another hunter--full penetration of the skull.
I've found that the solution to accuracy in with the PRB is to use the optimum load for the barrel twist, with a fast twist the optim load is lower and if exceeded the structural limit of the ball will be exceeded.
For big game hunting, the slow twist barrel with a hefty powder charge and a PRB are very effective with good penetration. I admit I haven't had a lot of experience with the conicals and I'm a 100 yds or less shooter with black powder.
Just my experiences and thoughts.
Shotgunman