For recreational/educational purposes, i am looking into building a small cannon which would shoot projectiles of about 1.0 cm in diameter. I would like to gather some information regarding the PSI needed to reach high velocities (roughly 100 m/s) with a projectile of mass around 7 grams. Should CO2 be used as the pressurized gas? Would anyone provide a rough outline on how i would go about building high pressure, welding the barrel, etc. ? Thanks.