I use up to 60 grains in mine with no ill effects so far.
I'm not sure what you mean by cut off the roundball, do you mean reducing the size of the ball?I know. The Walker could handle that load with no problem. The only problem was that I was busy shooting at the match with the Walker. Sombody offered me glass tubes filled with blackpowder with around 60 grain. He said when you use this loads you have to cut off the roundball to pusch this load in your cilinder. Nice offer but not during a match and I never cut of any balls.
Now that right there is funny!SO....if you do cut off the balls does the guns report go soprano...or is it high tenor ??