dp - A 1 1/2" group is very good at 100 yds for a ML. Heck I know some centerfire rifles that won't shoot that good. Striving for 'perfection' can be frustrating. I'd say that you remember that load that has given you those groups consistantly and play around with other bullets, sabots, load combos and see if you can get the groups any better. If not, I wouldn't worry about it too much.