I had a friend who did this with a co2 BB gun. Yes, the ones that fire metal rounds.
The guy shot himself in the finger with it, just to see if it would hurt. The BB got jammed in his finger and he had to be rushed to the ER and had surgery.
i love it when people who don't know anything about airguns shoot themselves, thinking it won't need serious loving medical attention
airguns are amazing and surprisingly lethal, especially if it's pellet; i have a few of them, one being .177, one being .22 (5.56mm) and one being .25 (6.35mm), and i have no doubt they could kill someone at 40 yards
and even my $30 crosman bb gun could kill someone at five yards if i aimed it well enough