The .58 will be most definitely more powerful than the .54, if the balls, or bullets are sent out at the same velocities. Try using Killing Power to analyse the results. Velocity times Weight, time caliber, divided by 100 = KP. Not, this formula gives equal weight to caliber, and velocity and weight, which is just as arbitrary a formula as Ft. lbs. will be.
The one caution that can be stated about the .58 is that being a bigger ball, its takes more powder and maybe even a longer barrel to get the same velocity you can get shooting a .54 RB. And, because the .58 RB is heavier, its pulled down by gravity faster than is the .54, so that you are not going to get as flat a trajectory shooting the .58 as you would the .54. However, the difference is measured in inches, NOT FEET, at 100 yds, and for the most part, most shooters can't hold much finer a sight picture at 100 yards, using open sights, than about 3 inches. Throw in the excitment and adrenalin from humping the boonies to get into position for a shot, and then take the shot off-hand and a 3 shot group capability off a bench rest on a calm day becomes a 10 inch group if you are lucky. Fortunately, most big game are shot at under 100 yards, and most hunters have the good sense( and ethics) to pass on shots that are beyond their capability. That moose has a 20 inch diameter heart/lung area kill zone on a broadside shot, so You don't have as much to worry about hitting and killing a moose as you would a smaller, whitetail deer at the same range.
Forget about high speed loads with that .58. Concentrate on working up a load that you can shoot accurately under a lot of variable conditions. That heavy ball will go through game like a freight train through a passenger car. I you don't believe me, just do penetration tests in whatever medium you are comfortable using. I made a test " box " of 1 inch pine boards spaced and Inch apart for my testing. I used some modern rifle cartridges to establish some comparative norms, and then shot target and " hunting " loads through my .50 caliber rifle. The first deer I shot was at about 40 yards, and my ball broke through a rib going in, passed through both lungs, and some major blood vessels above the heart, and broke another rib going out. That is a 175 grain RB compared to 260 gr. RB. The balls went through 6 inches of pine wood, and the 6 inches of air in between, stopping at the 7th board. The ball was a flattened, distorted piece of lead, hardly recognizeable as a round ball. The velocity of the ' target " load was about 1425 fps. and the velocity of the " hunting load " was about 1975 fops. Both balls penetrated the same amount of boards and air.
I would expect, from observing the damage done to m club's backstop by .58 caliber ROUND BALLS, that your round ball load, at any reasonable velocity, will completely penetrate a moose in a broadside shot. If you use, instead, a conical, you may be able to penetrate the length of the moose with your bullet on a frontal chest shot.
