Mirrors are not an effective defense against military lasers. The power levels are too high and dielectric mirrors only work over narrow wavelengths. In the specific case of US military tech, some of the platforms use white lasers such that even dielectric mirrors are pointless.

I would try a shotgun style subsonic load with an adjustable fin/spoiler system that can be calibrated relative to the range of the target. The projectiles fin would flare out to reduce speed as it approached the target. Then an explosive charge would release a spray of super glue or pancake syrup, or something to gunk up the mechanism or disrupt the airflow on the propeller.