Look foward to more intense regulation of ammunition.
Yikes!
Reducing the scale of a CLGG to hand functional would alleviate concerns about being cut off with a roll your own solution. Per the developer functionality was achieved for self loading, field generation of propellant, barrel longevity, and operating systems. De-rating from the 15 mm prototype to a usable scale of practicality would be the challenge.
http://en.wikipedia.org/wiki/Combustion_light_gas_gun
http://www.amazon.com/Ballistics-2011-26th-International-Symposium/dp/1605950521