Propane
The most common fuel of high tech builders. Often metered into the chamber at 4.2% by volume, because you lose power if your fuel/air mix is wrong. However, it can be manually added trough (for example) a non-lit propane torch, as you would with an aerosol. The torch head mixes the propane with air, filling the chamber with a finished mixture, so overfueling using this method isn't a problem. This is especially convenient in pill bottle guns, where traditional metering isn't practical.
Propane is often the primary propellent in aerosols, it is also sold in bulk tanks and disposable canisters.
