Re: only .22?!?
Doubtful that it was an AR15 style rifle. They're typically chambered for 0.223 (same external dimensions as 5.56 NATO) rounds (up to about 29 grains of powder) whereas a .22 is shorthand for .22LR cartridge (up to 2 grains of powder). That said, there are some modified AR15s chambered for .22LR for silent or cheaper target practice. The energy of .22LR from a rifle (10" barrel) is about 60% more than that from a handgun (3" barrel).
Biting the hand that feeds IT
