Well, I don't have the money, or the equipment, or the room to make a hybrid gun (100x+ mixture), the best I could do is make the 3D plans and see if some CNC shop could make the parts.
But I was thinking about how to make one of those without requiring fuel cylinders, since those could be regulated in some countries and are "dangerous and scarier" than oxygen cylinders. Not only that, but loading the fuel and then the oxygen or vice-versa could be dangerous, it is better to gave the gasses separated, and mix them the instant you shoot the gun.
So I have an idea to make my own hydrogen cylinders, the idea is to use a metal (of course everything should be high tensile strength steel) cylinder with an aluminum burst disk (I'll explain later what's that for).
The cylinders should be filled with methanol, and have a heater inside, (like the igniters in high-mixture hybrid guns), then the heater should decompose the methanol into formaldehyde and hydrogen. Formaldehyde has a critical point of 408K, so it should stay as a liquid at the bottom of the cylinder when it is cold after the de-hydrogenation, while the compressed hydrogen should stay at the top.
Then the cylinder (which could be reacted while attached to the gun), has a burst disk, the burst disk is between the cylinder and the combustion chamber, which is then filled with air or oxygen.
Since the compressed air would relax the burst disk, it should make the gun even safer.
Then, to shoot the gun (which has a burst disk between the chamber and the barrel), we simply vaporize the burst disk with electricity, thus mixing the hydrogen and the air, and igniting them. This is a hard part, since the burst disk flexes it would be hard to keep contact with it, maybe the electrode should be a spring.
The hydrogen and oxygen should react immediately while the liquid formaldehyde stays at the bottom of the cylinder, it should start leaving way after the projectile leaves the barrel, creating a nice muzzle flash. From the calculations I did, the energy form the hydrogen should be 6kJ per gram of methanol.
I think the hardest part would be ensuring the reaction happens at high pressure, since it should make it thermodynamically harder. However it is already hard at atmsopsheric pressure, since it it endothermic, The heating plays a big role in the reaction. And I'm pretty sure it would happen at high pressures, but the temperature required might be so high that you could get CO and H2 instead of formaldehyde and H2, that's a problem since CO has a very low critical temperature.
