Want an M16? Print it. Actually, it’s just a .22 cal. pistol, but it works. Printed with an old Stratasys 3D printer, it cost about $30 – but some of the new printers could bring the cost down to $10. Difficulty: you’ll need to find a steel upper for the actual shooting, which drives the cost up just a bit. With tech improvements, though, gunshops could soon be candidates for Jurassic Park.