Hello , I love target shooting from my garden, but was always upset by the noise of the .25 pellet hitting the target paper.So I decided to build a box from 1/2" plywood , insulated inside with soundproof foam and filled with linen and sand bags . Target is 5" inside the box ( maintained by 4 magnets) , and the box dimensions are 25"X12"X15". I put a cover with a plexiglass window over the target to give some light.Now I can shoot all day long without anyone knowing it.Here is a picAldea6
Rubber mulch is another good alternative, and easy to clean too! Just dump in water and the mulch floats/lead sinks.