Well, I don't know about hot air, but there was a hell of a lot of cold nitrogen whooshing around my back yard this morning, accompanied by copious amounts of wood and glass shrapnel, as well as about 30 pounds of steel plate.
The following is my entry for the "Best Shot on Video" competition. The angle kind of sucked, but, as you will see, I couldn't really reset and try again...
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In case you didn't read the video, the projectile weighs 1130 grams, and is an old disposable oxygen cylinder filled with ice. It travelled at ~385fps, for a muzzle energy of >5700 ft/lbs

. The firing range was 13', and the target was a solid wood door with 1/4" thick hardened steel plate armour. As far as I can tell, when the slug hit the steel, instead of stopping, it caused the entire plate to rip through the door, shattering the door and carrying the steel plate into my shed (which survived without damage, despite JSRs continually ominous predictions).

Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.