Actually "screaming his head off" would to me indicate that he was high as a kite on something - crack, heroin, meth, who knows? Probably didn't know he'd even been hit until he fell. Certainly must have been feeling no pain.
Whether he knows he's been hit or not, whether he feels the pain or not will be a secondary consideration when he is laying flat on his back in a pool of his own blood, unable to rise again.
That's why I have the .44 mag.