Definetly check out the Aguila colibri ammo! I shoot it in my livingroom all the time! It goes about 1/2 way through my local phonebook. I just set up the target across the room from my sofa,and blast away.Lot's of fun when you can't go outside and shoot.I buy the higher power version(orange box) as opposed to the lower fps version(yellow box),because it seems to be more accurate.This was confirmed by the people who sell it,as they think the higher fps keeps it on target better.Also,pistols are alot louder than rifles,maybe a little louder than a powerful pelletgun.
Take that mini apart and grab your dremel and polish some of the metal to metal sliding places,like hammer face,bottom of the bolt/carrier where they contact the hammer and slide over it while going back.Look it over and you will see other places where you can polish. I use a polishing(cotton)wheel and some compound.