Watch this short tutorial on how to make a realistic bullet hit to simulate an actor getting shot by a gun. Materials needed include a pressure sprayer, clear tubing that will fit on to the hose of the pressure sprayer, a small Translucent PVC elbow, fake blood, duct tape, a funnel, a shirt you don't mind damaging.
First, fill the tube with blood, and then tape it to your actor. Cut an x in the shirt where you want your person to get shot.
NOTE: This effect works best if you tape the tube to the actor's body, then tape the end of the tube where the blood comes out to the inside of the shirt. That way your shirt doesn't puff up or anything weird, and that way the blood is guaranteed to come out of the shirt.
Second, either you or someone else must pump the sprayer about 140-200 times, this will probably vary depending on the sprayer used.