I want a .50 cal M2 and a 60 mm Morter. If the government can have them then I need them too!
Combustion-Light-Gas-Guns, a technology competing with the Rail-Gun, were developed for the U.S. Navy’s consideration. First prototype was 15mm and stepped thru 45mm. to 155mm. pieces achieving 2.5km. and 4km. velocities. Consistent ranging at 100 to 200 miles were problematic using gaseous fuel mixes in artillery. Definitely not a spud-gun!
http://en.wikipedia.org/wiki/Light_gas_gun
http://www.utroninc.com/tech.html