That's a common experiment, with some merrit, if other projectiles of known performance on deer or moose are also tested. that way, a co-relationship of perfomance can be made.
A friend of mine in Idaho does exactly that on his ranch. He's found that that milk jugs of water, with 1/2" plywood between them gives virtually identical performace of expansion and penetration to what he sees from his modern guns of all calibres and loads and also includes .45/70 factory 405gr. jacketed ammo results in elk, deer, bear and moose.
Unfortunately, the nitroexpress sight was hacked and is gone now as that's where he published all his data. I have some saved, but since he isn't a muzzleloader shooter, he has no such data. The value of this information, is that the resutls in this media closely approximates in what he sees in game. Therefore, it should be of benefit to duplicate his tests with our RB guns.
The same criteria could be used - milk jug, plywood, mild jug, ply wood, etc., etc. different balls, alloys, etc. With a .526" bal in a normal .540" bore, just about any alloy could be used, inculding WW for deeper penetration if desired.
It would be very interesting to shoot Keiith's .75 into that media - as with any more than 120gr. 2F, he couldn't keep WW ball inside a moose.