Ballistics testing for the military is an expensive proposition. A potato cannon, popular in at-home ballistics testing, is cheap. A new testing device developed by the US Navy — a supersized version of the spud gun — provides a low-cost alternative by simply shooting stuff out of a few pipes.
Developed at the Naval Air Warfare Center in China Lake, California, the Variable Energy Research Accelerator (VERA) is a transonic impact gun for use in ordnance development labs. It's built to launch live or inert missile and bomb components at transonic speeds — just below the speed of sound. It's much less costly than other methods, like rocket sled-testing, which can require modifying structural components to fit on the sleds.
The gun has a 12m long barrel and a 19-inch (48cm) diameter bore, which is very useful for shooting oddly shaped projectiles. According the YouTube videos's poster Inigo93,
It's what's known in the potato gun world as a hybrid. It uses both compressed air and combustion to operate. Basically, throw some compressed air and fuel into a chamber and light a match. 'Tis very similar to the inner workings of an internal combustion engine. I just use propane instead of gasoline and my "piston" isn't attached to a crank shaft.
VERA can fire projectiles weighing up to 90kg with as much as 2.25 megajoules of energy — that's shooting a 45kg load at 300m per second. The speeds, on the low side for muzzle velocities, allow the gun to minimise acceleration forces to less than 600Gs, enabling testers to accelerate loads more smoothly than with conventional powder or compressed air methods.