Arcticap has it right, it's a parallax thing. Shotgun, muzzleloader and .22 rimfire scopes are usually set at 50 yards, sometimes 75. I wouldn't hesitate to use the scope on a ML.

I'm no authority on parallax or the physics of optics, but it would seem to me that when you're shooting at a 50 yard target with a scope that has a 100 yard parallax set, you would have about the same potential erroras shooting a 100 yard target with a scope with a 50 yard parallax set. In both cases I would think the effect would be very minor.