[zorg]

iirc, there was an explanation in the Guardians of the Flame series where the mages guild created guns in a very similiar way. It was a rather convoluted setup where, similiar to the ideas here, water got superheated in a metal casing, and the casing held together with magic. Somehow they ended up with a highly pressurized bullet, which somehow released this energy upon contact with water (which had been defined as breaking the enchantment holding everything together).

As I said, it was a bit convoluted. Also, the mages guild in the books never was able to mass produce these wizard guns. Still, the description in the books might be of interest.