For your next project, a hydrogen gas gun. I once knew a rocket scientist developing a gun to fire satellites into space. I only got to see a bar napkin sketch of how it worked, but but the gas fired a piston that compressed air and the compressed air fired the projectile. Granted they were working with a gun the size of a small airfield, they were launching a watermelon seed shaped projectile at Mach 6-7. They were aiming to hit 9. Don’t quote me on the numbers…it’s been many years since I got this info. And it being on a bar napkin, there was likely alcohol involved.