...the percussion revolver is simply not defined in the code...
Well then from a legal standpoint, if you use it and claim it's a
muzzleloader and a judge agrees, then it has to be .50 caliber. If you claim it meets the requirements for a
modern revolver, you are then excluded from muzzleloader season.
However, I think you run the
huge risk of a judge determining that since it isn't
defined in the regulations, nor is it specifically one of the firearms
enumerated for use during any of the hunting seasons, it does not fall within a
legally accepted method for taking game, and thus is altogether prohibited.
For example, squirrel are not listed as a "fur bearing" animal in the hunting/trapping regulations in my state. They may be legally taken with various firearms, but they are not listed as trappable. So...say a hunter put out a few modified rat-traps, on some leaning trees, baited with peanut butter, and then moved off to do some deer hunting, returning later to collect the squirrels? Somebody might determine that since squirrels in the wild are not listed as legally trapable, even though it doesn't say they can't be trapped AND even though it's not illegal to dispatch a squirrel that has invaded your attic with a trap, that taking squirrel by trap is not a legal means. The same might be had for that "gray" area of your revolver.
You could also just not worry about it unless a DNR person questions you about it. Just document how many times and from whom you got an answer other than "nope".
LD