Mix a bottle of the flour, water, and food coloring together. Add more food coloring if needed until you get the red blood color that you want. This will make enough blood for 10 to 15 gunshot wounds.
Pour the fake blood into a latex condom and tie the open end. Try to fill the condom a little more than 3/4 of the way with the fake blood so it will have enough pressure to burst.
Tie 10 feet of fishing line to a washer. Now glue the washer to the latex condom and allow the two to bond. With the bond between the condom and washer complete, put your victim in place. Tape the latex condom under the actor's clothing using duct tape.
Cut a small piece from the actor's clothing over the area where the condom was placed, uncovering the metal washer. Set the piece that you just cut out over the condom and washer to hide them from the camera.
Begin shooting the scene. When it is time for the actor to get shot, pull the fishing line that is attached to the washer and record as the blood flies everywhere.
Add the gun effect. This can be done by shooting a gun at the same time you pull the fishing line. You could also add a gunshot sound in the editing process. Just match up the sound with the visual of the blood.