The ornamental design for a muzzle loader loading tool, as shown and described.
FIG. 1 is a perspective plan view of a muzzle loader loading tool showing my new design;
FIG. 2 is a perspective bottom view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof; and,
FIG. 5 is a front elevational view thereof, the rear elevational view being a mirror image thereof, the right side elevational view being a mirror image thereof, and the left side elevational view being a mirror image thereof.