A 2 liter pop bottle will greatly reduce the noise made by a .22. You can even find devices online that aid in attaching such bottles to rifles. They only work for 1-3 shots, and you still need to shoot sub-sonic ammo, or it's going to be pretty loud.
If you want a silent .22, get the Aquila 550 fps powderless .22 LR rounds. They work off the primer alone. I shoot mine in an old Savage Model .24 rifle that has a very thick barrel (it's a .22 over .410 and the .22 barrel has the same outside diameter as the .410).
The only noise this gun makes with these rounds is the click of the hammer, then the thump when the bullet strikes the target. It makes about 10% of the noise my RWS Model 34 .177 cal air rifle does.
It's a deadly round, too. I killed two 20+ pound coons with one shot each the other night. The loudest part was the coons hitting the ground from 25' up in the tree. The rounds entered just below the eyes, and didn't exit, but obviously made it to the brain.
· 1 decade ago