How do film makers fake actors getting shot?

How do film makers fake actors getting shot, especially in the head, and make it look so real? A scene I particularly have in mind is from The Departed when Billy Costigan (DiCaprio) gets shot in the head. Thanks guys.|||There a pipe strapped to Leonardos back running all the way up to behind his head, its only like 20-50mm diameter and has a bend so that it is directly behind his head but aimed away its usually attached to a high pressure cannister, at the bottom out of the shot of the screen. and they just remote detonate so all the blood looks like its coming directly out the back of his head. His jacket and the camera angle disguise the effect. The entry shot from the front of the head is a digital effect (this was first used in Saving Private Ryan).





Another way they do for example in the film Goodfellas is they shoot the actor and then someone is just to the side of the camera and has a paintball contraption advice to shoot blood on the wall behind the actor in synch with the blank gunshot that is fired so it looks like one smooth realistic shot. For the front of the face they shoot low pressure fake blood onto the actors forehead or might have a string with a red blot of blood that they pull off the actor and shoot it in reverse so that when it is sped up and edited it looks like the actor has been shot in forward motion.|||It will depend on how they shoot it and where etc...





They'll often use things called "squibs" which is a small amount of explosive. So small it would not hurt the actor or stunt person. T





They will also have little blood bags (the size of an un-blown up balloon or smaller) and when it goes off, the "blood" (syrup and colouring) is released...