The Walker has larger chambers. I am reading that the ROA has a 37 gr suggested capacity, with Round balls, you can stuff 45 gr under the ball and still turn the cylinder. Hmm...1150 fps. The Walker will hold 60 grains. Do the Math.
I dump 40 gr in this '58 and compress it and there is at least 1/8" of free chamber. I'm guessing that the ROA and 58 probably have the same size cylinder. I dont have an ROA to compare to.