Coil gun!
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The efficiency is rather low, so the energy of the projectile is about 37 joules. This is not very potent compared to a real gun. In comparison, a .25 ACP (saturday night special type of gun) has about 85-140 J, a 9 mm (parabellum) has 300-500 j and an AK 47 round has about 2000 J
But it's pretty cool he made it himself.