What brand and model of scope? Same on both rifles? Sounds like a warranty issue to me. No quality scope should be beaten to death by a few 100 rds. of low-powered rifle ammo.
The minis probably have a slightly higher reciprocating mass than the AR, which might mean that the forward impulse of the action closing is higher, and that can be rough on scopes (supposedly this really affects scopes on spring piston air rifles which sort of recoil "backwards"), but that shouldn't be enough difference to kill a scope.