I avoid gasoline due to the handling issues. It's messy. I tend to get it on my hands even when refilling my lawn mower. And the vapors/odors from gas linger for what seems to be "forever".
But I mostly worry about ignition of excess airborne gasoline vapors....
On one extreme, I've read in the paper about someone using gasoline to saturate wood prior to starting a large bonfire, and the vapors in the air ignited and led to significant injuries for people who thought they were standing a safe distance away when the fire was first lit. I recall that the injured individuals were thought to have inhaled airborne gas vapors before the fire was lit, and the most severe injuries to these people were from the burning of these vapors inside their lungs.
I've personally used gasoline to burn out yellow jacket nests in my yard. For folks unfamiliar with yellow jackets, they are an agressive type of bee that create their hives in the ground. When I've torched the nests, I've poured a cup of gas down the main hole, retreated a good distance to light up my torch on the end of an extension pole, and then touched off the gas in the hole. I often see jets of flames from the hole which run along small valleys in the surrounding ground (thus my use of an extension pole to light), which I think must be excess gas vapors drifting and pooling in these low areas.
For spudguns, I think I would mostly worry about people spraying gas into a chamber with a cheap spray bottle--it might be safe for a while, but eventually someone stands a decent chance of getting burned. Maybe a little excess gas on someone's hand or a flannel shirt sleeve, then as the person holds the launcher they accidentally place their hand near an exposed electrode on the launcher, and with a clikc of the ignitor there is a spark and the burn begins.
Now, if a non-messy way to use gasoline in a spudgun can be devised, then that would improve safety. Maybe something like a carbuerator jet combined with a small hand pump can be used to meter gasoline with no direct human contact? It might be a fun challenge to build, but I don't see it as a mainstream way to power spudguns.
Finally non-related comments. I can't wait to see your hybrid BigBang, especially now that you've teased us with mention of a unique fueling system. As for the combustion model Hall was working on, I agree that it would be great to see it happen some day. I think most of the strife was caused by folks (like me) who argued with Hall about fueling proceedures for hybrids. This is unfortunate b/c in reality very few people have hybrids, but a lot of people could make use of a standard combustion modeling program. If Hall reads this and is inclined to re-start, I can try to produce data to validate the model.