A powder gun like the one used in Harp and a gas gun like Sharp both work in the same basic way – expanding gases. The lighter the gases molecular weight, the f

A powder gun like the one used in Harp and a gas gun like Sharp both work in the same basic way – expanding gases. The lighter the gases molecular weight, the faster it expands in air. Gunpowder has a molecular weight of 22, slightly less than air at around 28, but ignited gunpowder is incredibly hot, so that’s why it expands so quickly. The hydrogen used in gas guns, however, has a molecular weight of two so expands extraordinarily quickly in air. I couldn't understand from the article how the hydrogen was being used in a "gas gun". Since pure hydrogen doesn't ignite, wouldn't we care about the molecular weight of the oxidizer as well? It turns out the "light gas" is important just for it's low molecular molecular weight. It's never ignited, and one could substitute Helium for Hydrogen if one wanted. The gas is a second stage in addition to, rather than instead of the gunpowder. It's like a spring-air gun, but instead of spring you use an explosive charge. Here's Wikipedia: https://en.wikipedia.org/wiki/Light-gas_gun https://en.wikipedia.org/wiki/Light-gas_gun And here's some PVC experimentation: http://www.chrisfenton.com/2-stage-light-gas-gun/ http://www.chrisfenton.com/2-stage-light-gas-gun/