A potato gun with hair spray as a propellant can for sure kill a man. My friends in high school would make them, and blast a large potato 2-4 football fields.
be careful with these if you get too extravagant. the only thing keeping this from being considered destructive device is that its a smoothbore muzzle loader.
if you were to put a bolt action and or a potato hopper on it or rifle the bore it would be a DD , stay on compresed air if you want to mod up. other than that, smooth bore shove a spud in the end and light up with butane and its a legal device
Hehe, I did professional CAD for a year before college so that whole thing is custom drawn in AutoCAD. As in I hand measured and drew each part because I didn't have some library of parts. It was part of my senior computer science/writing (lol) project 18 years ago. It's sitting in my dad's garage 2,500 miles away. A writeup without some action video would be kind of boring and I don't have the tools or space to build another in my broom closet of an apartment...
You're welcome to build one yourself with the spec and do it. The only things not shown are:
1. An ordinary Schrader (bike tire) on the tank. Drill through the triple walled part somewhere, tap, Teflon tape and twist it in.
2. A 0.25" NPT ~125(?) PSI pop off valve also in the triple walled part (somewhere) and maybe a pressure (I think? The bike pump's gauge should be fine as long as you don't fill it with really cold air and then leave it in the sun). Technically optional, but if you explode yourself it's on you.
2. The battery box to activate the sprinkler valve, but that's just a couple of 9v batteries in series in a project box with a big red button. I never even bothered mounting it to the gun so it just kind of...dangled from the gun by its wires.
3. A wooden block cut to fit between the barrel and tank with a semi-permanent metal strap around it to hold it together. Very solid with this, very janky without it.
Both ends of the sprinkler valve are just sealed with teflon tape and twisted together so You can take it apart for transport.
To assemble the nested barrel I left the 1.5" SDR 21 outside during winter and filled the 2" SCH 80 PVC in the shower with hot water (sat it on the drain plug), then slid the little one into the big one. The 1.5" SDR 21 was hand picked (mic'ed) to closely fit in the outer barrel by the guy I bought it from. You might not even need the outer barrel, but 1.5" SDR is really thin, so the chonky outer barrel protects it.
I played with it up to ~105 PSI, but it could probably handle a lot more without the pop off installed. The U-bend hampers the hell out of the flow, I'm sure, but a 10' long gun would have been very awkward to move around and be hell on the all the component joints. As is, you can hold it like a big minigun and shoot it. Though the cyclic rate is about 1 round per 5 minutes depending on how tired you are on the bike pump. Recoil is negligible. It'll punch a golf ball through 1" of chipboard, who knows what else. Maybe a person.
After the initial discharge the sprinkler valve flap makes a hilarious hooting noise.
Maybe I'll see if the Backyard scientist wants to recreate it? It seems right up his alley.
I did something very similar, but used a butterfly valve rather than a sprinkler release. It meant needing to stand next to it and manually release, but it was a lot cheaper.
I also used 3/4" piping, which worked really well for lots of smaller projectiles, and meant that a female threaded adapter and some epoxy let me use 20oz or 2 liter bottles as tanks. I only got them to 80 psi, but I suspect they would have held just fine at 100.
Soft projectiles would disintegrate in the air (no paintballing) but hard things- gobstoppers, batteries, frozen grapes- could cause a lot of fun destruction.
