Sure, the plastic skirt or belt expands to fill the bore but if the copper bullet is only .499 and the barrel is .504 it can exit leaning (canted) at an angle and this may greatly affect accuracy.
That would be a big bore for a modern ML.
Just for some info. The Platinum and Aerolite Powerbelts fit tighter than the rest of the PB's. That's my experience anyway.
