A Mini-14 is way louder than an AR, I think it's because the bolt is recoil operated insted of gas, and all of the pressure goes out the front of the pipe. I remember shooting my Mini-14 at a indoor range, and the people on either side of me packed up and left. You may also want to try a black powder rig, but insted of wasting lead, try a plug of wax paper, I took out a hornets nest with one and it made my ears ring and dusted the nest without scratching the paint on the shed.