A Guacamole Gun is a small device that is used to simulate bullet hits without the need for squibs. The gun usually consists of a barrel, normally made of PVC pipe, and some sort of tank to store air. The Blood is loaded into the pipe and the pipe is fired towards the target just off camera. The most succesful guacamole guns use air compressors and a release valve to blast air down the tube launching the gore.
In a pinch it is possible to modify a garden weed sprayer and generate pressure manually, whilst this is time consuming it is preferable in a situation where power is not available. The weed sprayer is also the cheaper of the two and can be constructed simply by attaching the PVC pipe above the spray trigger and removing the smaller pipe that comes with the sprayer. The weed sprayer method also allows for a secondary technique in which a small tube such as a tropical fish tank airhose can be concealed on the body of one actor whilst blood is pumped from off screen to simulate a throat slice or similar effect.
The air compressor Guacamole gun can also be outfitted to achieve a number of different spray patterns depending on the pressure, length of tube and the consistency of the liquid. By changing these variables, the pattern can change to simulate that of a shotgun, pistol or a sniper headshot.
These types of explosions are generally favoured by low-budget filmakers, due to their relative safety, and their affordable prices. Costs can be lowered significantly as there are minimal insurance costs and decreased setup time. It is possible to simulate certain larger scale explosions using the same method. Using flour, thin dirt, or painted polystyrene chunks, it is possible to replicate small explosions, bullet hits and broken windows.
Flammable materials have also been used, with great results but with significantly higher risks and a greater need for planning.
Details on how to make such devices may be found below.