Thinking of assembling a steel bbs launcher, powered by a small jet engine of the compressed air-gas type.
Compressed air is not used directly to power the bbs. Before, it is introduced into a combustion chamber that burns the air mixture. butane, continuously, producing a jet of gases at very high speed, which is what would be used to drive the steel bbs.
The weapon is like in the video, the idea I mean, and the concept is like in the other video.
I have built a small engine of this type of reaction in the past, and the speed of the jet, with a convergent-divergent nozzle, is supersonic. The job is to be able to reliably turn the jet on and off, which can be done. It's actually a fusion of a hybrid with a full auto bbs launcher.
I imagine that the steel bbs, (so they do not burn), should be ejected at very high speed through the barrel.
For reference, my rc turbojet has a nozzle diameter, (sub-unique convergent), of 40 mm, and the exhaust gas velocity is about 900 km / h. With a fair length barrel, for example, you should propel a golf ball with good speed.
The classical system
The power source. Observe how the nozzle of the albatross literally shoots soccer balls, tomatoes, packages of flour, and I don't know how many things other than these crazy insane, couple to the jet of the jet fighter.
What I think is that you can significantly increase the speed of the air coming out of the pressure tank, heating it. It's like an afterburner. The increase in flow velocity depends only, in general terms, on the initial and final temperature relationship.
For example, if the air leaves a tank at 7 bar, and has a speed of 120 m / s when expanding in the barrel, with a temperature of 20 ºC, Ti, (293ºK for the calculation because it is absolute temperature), and we heat that air with a fuel at 1500ºC, Tf, (1773ºK), as in a hybrid but continuously, the final speed will be the square root of Tf / Ti, which as a result gives 2.45. The speed of the superheated air would increase approximately in this percentage, 245%, about 294 m / s ... It works the same as an afterburner. For the rest, first idea, it is only necessary to interrupt the air outlet and combustion process with a trigger. It is somewhat of a hybrid because it uses compressed air and a fuel, and it could be a burst weapon.
The increment is as in the drawing, taken from a jet engine article.