Aquanet?
My friend Dave and I use engine starting fluid.
Ether.
Well? It's ether Aquanet or starting fluid. Make up your mind!
:P
If you are going to piddle with higher octane fuels, i recomend building your spud cannon with ABS piping.
Pfft! Build it out of drill stem. With some drill stem, old Caddy parts, a welder, pyrodex, and plenty of beer, you too can build an extremely dangerous cannon that the Sheriff will ask you to stop shooting because you're a drunken redneck idiot bent on accidentally killing yourself. Substitute some acetylene for pyrodex (and sober up) and he'll cool off about it and maybe even ask to shoot it. Use electric window motor parts for a T&E mechanism, weld in a piston (after some grinding) for a breechplug and firing chamber all-in-one, and set the puppy off with a rocket motor igniter. You'll need a wiring harness or two to make a long enough ignition wire that you can run it into the trench. You'll definitely want the trench.