think about it, if the tank is pressureized, it will be harder to dent and damage, the psi is not large enough to explode by a puncture, if ya want to see what happens, take a old propane tank, fill it with air to the psi desired, and go shoot it with a nice size rifle, make sure ya are away from anythgin, i aint exactualy sure how the added pressure will affect the penetration, as for shooting steel, i shoot 1" plate plingers out on the farm and the military guns go through 3/4" and its safe.. about 100 yrds...
as for a compresor, couldnt ya use a a/c compressor, that is if ya want to...