I confess that I've not really thought about the details of the valving since I doubt I'd get the funding to build such, burst disks work well, and burst disks are a negligible cost in the Big Picture. The point being that whimsy aside, the gun would almost certainly use burst disks. With the valve ...

I swear to all things holy and not, if I had the money lying around, I'd build it. I would actually be crazy enough to go through with building this thing. It would be absolutely hilarious. Let's just say that I didn't come up with the performance specs on a whim. I was asked by some folks if it wa...

You're not going to get much lower friction than teflon seals, but they can still be a bear to turn. Ball valves simply aren't designed for quick/easy motion.

Turns out that the same guys who run the Cowboy Shoots also do what they refer to as BAM shoots.... Bolt Action Military. Basically the idea is to use a bolt action military rifle in as-issued condition that dates to 1945 or earlier. It also turns out that my Mom once bought an 1895 Mauser on a whim...

The purist in me loves the idea of a port that is actually larger than the bore, with the breech tapering down such that flow into the bore is smoooooth and maximized. But yeah, the realist in me realizes that for the vast majority of cases this is beyond overkill. Hmmm... Let's see if I can come up...

Some more thoughts on the thought experiment.... It assumes constant density, but this is obviously incorrect. But what DOES density do? In the first moments after the valve opens, not much. Constant density probably isn't a bad approximation. But as the projectile accelerates we know that pressure ...

I'm sitting here looking at a piece of 38 special brass. It just happens to be on my desk (yes, really). And I'm thinking to myself, "Self, this might make a good projectile." More to the point, I could see epoxying a nail in the primer pocket to make a dart. But a dart that is reasonably cheap/easy...

...I'm still pretty pleased with these two pics I took tonight.

Probably the quickest/easiest hand calcs you can do for potato gun prediction.... EndPressure = StartPressure * ChamberVolume / (ChamberVolume + BarrelVolume) MuzzleEnergy = (StartPressure + EndPressure) / 2 * BarrelLength * PI/4 * BarrelBoreDiameter^2 MuzzleVelocity = sqrt (2 * MuzzleEnergy / Proje...

I looked at the GGDT program and it doesn't appear to have an option to calculate the maximum range in which it will be able to fire which is in my opinion the whole point of the software.. The point of the program is to have an idea of what your muzzle velocity will be. As for maximum range, that ...

This is one of the few examples I remember of a publicly available paper from Utron's contracted government research project for a "Combustion Light Gas Gun" (CLGG) - A.K.A. a badass hybrid that many strived here to get close to. Full paper here: https://apps.dtic.mil/sti/pdfs/ADA462130.pdf There i...

I realize there are people out there who are much faster than I am, but I was pretty proud of this run.....

[deleted for reasons]

As far as I'm concerned.... If you're using hair spray or any other "aerosol" that isn't intended for burning, you've failed to do any meaningful research on the topic of spud guns. DITCH THE DAMNED "AEROSOL PROPELLANTS"! Propane. In a pinch, butane. If you find yourself in a 3rd world country with ...

Yeah I thought about this too but it would have much more friction and sharp corners would make it unstable in flight. It possibly could even desintegrate in air. Friction for any reasonable projectile is negligible in the "does this thing even work" sense. As for unstable flight, you're going to h...