I've had my Mini now since 9/11 (great day to pick up an awesome American-made classic, yes?) and I've run about 500 rounds of Brown Bear through it with no issues whatsoever. In fact, my Mini will chew up and spit out any ammo you put in it. PMC, Winchester, Tula, Brown Bear, Federal, Freedom Munitions, 556, 223, whatever. That's the beauty of the Mini.
Shoot it and enjoy it. If it gets a little dirtier, then clean it. The savings is well worth the extra time spent cleaning.