SpudFiles

This is just a spare parts gun I threw together last week. Chamber is 30 ci, barrel is .787" x 61".

Fired by opening filling ball valve, which fills the chamber to 500 psi in a few seconds. After firing, the valve has to be closed immediately to prevent very expensive and violent gas loss.

Muzzle energy is 410 ft/lbs @ 630 fps for 30 gram slug, and 460 ft/lbs @ 430 fps for 70 gram slug.

Pictures. The first picture shows the slugs I used. The little ones are 30 grams and filled with ball bearings, and the big one is 70 grams total and houses a 60 gram steel dart.

The valve setup.

The cannon resting on my hardened steel plate backstop.

Picture of the full cannon, in all its horribly discoloured glory.


And a few short clips. The first two shots are with the 30 gram slugs, and the last one is with the 70 gram slug. That board is made out of some strange material and is A LOT tougher than it looks.
[youtube][/youtube]

Hardened steel plate backstop?

Looks like a wooden board with a large hole in it to me

Mind you. I think you're a bit close to be firing at a steel plate. If I'm firing at close range I use a tunnel of fibre mat to catch the inevitable rebound and since I've found riccochets buried deep in the lawn I'm a bit cautious about it.

The firing shots sound pretty nice. A more sophisticated disk mechanism might be a good thing if possible.

416 FPL ?!!111ONE??? Amazing! Are you using CO2? What do you use for the burst disk?

The plywood with a hole in it is just what I hang the plate on. The plate doesn't cover the whole sheet of plywood, so you can see through the hole.

I wasn't firing at the steel, I was firing at more than 1" of the mystery board mentioned in my original post, plus another 3/4" of plywood.

416 FPL ?!!111ONE??? Amazing! Are you using CO2? What do you use for the burst disk?

The power isn't really that exciting. The SCTBDCv1.5 will do over 6000 ft/lbs (no typo).

CO2 is one of most useless gases conceivable for pneumatic propulsion. I use a 2400 psi industrial nitrogen tank regged down to 500.

The burst disk is 16 layers of aluminum foil, which generally fails between 450 and 500 psi.

Thats pretty cool.
I like the part in the video when one of the projectiles rolls in front of the camera, it's like one of those tumbleweeds in those westerns that always roll across the street before a duel. Clearly the plywood lost this one.

holy s#!t. i like it alot. but i'm not to sure on your filling system. wouldn't it be better if you filled the camber then used a ball valve to crack the foil? because you might not be getting the pressure your thinking

Again, that poor shed, but it shows that with a bit of high pressure for brute force, you don't need a sophisticated construction

holy s#!t. i like it alot. but i'm not to sure on your filling system. wouldn't it be better if you filled the camber then used a ball valve to crack the foil? because you might not be getting the pressure your thinking

If I did that, the opening time of the ball valve would cut performance hideously. This way, as soon as the whole chamber reaches the right pressure, the disk blows. Kind of like pumping it until it bursts, but a bit more sophisticated.

Yeah, this is about as simple as it gets while still having semi-decent power.

can we get a picture of the burst disk bursted already

Why? It probably just looks like this.

Except with 4x more layers of foil.

wow my disk didnt burst like that mines ripped well i think thats beacuse i dont have a union yet its just clamped in threded fittings

Yeah... kind of off-topic, but the smoothest aluminum foil will ever look in it's life, (besides when it's already on the roll), will be when it's clamped in a union with pressure on one side. Makes almost a perfect convex mirror.

These came out of a steel union with a neoprene gasket to seal.

Mine uses a butyl rubber gasket and a steel union. I don't have any of the bursted disks around, I just throw them out when I replace them.

Most of my bursted disks just look like the one on the left of Mark's picture, but with four neat "petals" at 90 degrees to the rest of the disk.

In comparison, the front disk on the SCTBDC after a shot just looks like a perfect ring of foil. There are no loose pieces attached, just a thin ring where it sealed on the outside.

The past tense of burst is burst, therefore a disk which has burst is a burst disk, not a "bursted" disk - because technically, before it's been fired, it's just a... well, "disk"

This post was brought to you courtesy of the grammar Nazis

I used bursted to avoid confusion. You are slightly wrong though: they are called burst disks before they have burst, and they should be called "burst burst disks" after they have been burst. But that would get a lot more confusing than just writing "bursted disks", which is grammatically incorrect, but probably no more so than " burst burst disks", however not as much so as "bursted burst disks" (which is also slightly less confusing than "burst burst disks"). Chew on that one for a while JSR