Use carbon dioxide fire extinguisher for spud gun?

I have not tried shooting bits of potato, but did make a similar gun that fires a 1 inch diameter steel slug that weighs about a pound. The slug has a nylon cord attached to it and I can shoot it over branches high in a tree. Then pull a steel cable up and around the tree, so I can make sure the tree falls where it will do the least damage.

Do be careful. While perfecting this, I lost several slugs and worried that they may have landed in the neighbors yard about 500 feet away. And that was with the gun pointed nearly vertical.

Dan

Thanks, Dan. I wasn't thinking of firing steel slugs, just potatoes. Did you use a fire extinguisher for the propellant?

Best wishes,

Chris

Hi Bob,

Good to hear from you. The metering idea is interesting. I was anticipating just squeezing the handles until the projectile leaves the muzzle.

Best wishes,

Chris

Oughta work, Chris. Air rifles have been using carbon dioxide for years. Likely your problem will be "metering" the charge into the spud gun. Fabricate some sort of a hammer falling against a valve to meter a charge. Air rifles used to use something call "Hycar" as I recall. Think "O" rings, maybe.

Bob Swinney

Alter the stop on a ball-valve so instead of closed-open it goes closed-open-closed, and you can perfect the rotation rate of the valve to give the perfect push.

Dave

On Feb 28, 5:02 pm, "Christopher Tidy"

Yes I did use a fire extinguisher. I did not sqeeze the handles. I used my hand and bumped the moveable handle so the valve was only opened for a small part of a second. I used pvc pipe which has not shattered, but did have another pvc pipe surrounding the one used as a barrel. I don't think using just one pvc pipe is safe.

The only reason I used steel slugs is to have something to tie the string to. I started with a smaller diameter, but found I needed more weight to get the weight to drop to the ground after it went over a branch and encountered more branches on the way down.

Again be careful. There is a lot of energy involved.

Dan

Thanks, Dan. What fittings do I need to connect to the fire extinguisher outlet? Any idea what type of places sell them?

Best wishes,

Chris

I am in the US so it could be different elsewhere, but it was just a regular 3/8 pipe thread.

Dan

That's a possiblity I guess. But if I was going to build a metering system, I'd like to build one which doesn't rely on the user's skill or judgement.

Another option might be to have a small chamber which you could pressurise with carbon dioxide as a means of metering. But I don't like this idea much as it involves getting a pressure vessel.

Best wishes,

Chris

Thanks, Dan. I have a couple of empty 2 kg extinguishers. I'll try to measure the thread on those.

Any recollection of how many shots you got with your extinguisher, and what size the extinguisher was?

Best wishes,

Chris

Sure! Paintball guns use CO2. Do some googling and you'll find designs for fast-release valves that admit a metered charge. Some of them are like pilot valves that use the pressure of the cylinder to assist rapid opening of a larger element.

Gas flow in a feed tube cannot exceed sonic velocity, so size your feed accordingly to fill the volume behind the projectile.

A fully-metered system would be really neat. But I think the first step is to build a barrel and just see how it works with a squeeze of the handles. A project like this has a lot of potential for later refinements.

Your gas flow point is probably a good reason for buying a 5 kg cylinder rather than 2 kg. I think 5 kg cylinders have a wider outlet.

Best wishes,

Chris

How would you refill/recharge such a beastie? Would you refill the tank from a compressor?

Just curious

T

CO2 will give you appx. 4 times the volume of compressed air in the same cyl. When you are out, show's over. I built a pneumatic spud gun, using an outer chamber and a diaphram. Finding the right plastic for the diaphram was tricky, a few burst, some wouldnt flex, but the one in it, made from a storage box lid, has lasted a few hundred shots.

It will launch a spud at least 250 yards out fired at a 45 degree angle, and with a 1/2 inch bolt and washer stuck in the projectile will dent a dumpster. Serious hazard here, don't fire it skyward in a populated area. It only works with a tank or at the shop, but the machine shop i run is out on a ranch and the cows arent to many. It is too powerfull to use at home. I will have an air system on the rock-crawler Jeepster i am building, so that should be fun during breaks on the trail.

I would likely just take it to the local fire exitnguisher place. Getting them refilled is fairly cheap if they're young enough not to need a hyrdrostatic test. Otherwise I'd need to buy a diving compressor, and they cost big money.

Best wishes,

Chris

Stupendous Man sez: "> CO2 will give you appx. 4 times the volume of compressed air in the same

According to "Appleton's Cyclopedia of Applied Mechanics" in an article re. air motors, "Reservoirs -- Under ordinary conditions, the capacity of the reservoir should represent 10 or 15 times the consumption of air in cubic feet per minute when the air is used variably, as in rock drills; in cases of regular employment, 4 or 5 times the consumption per minute may be taken as the rule.. . ."

That deals with air motors, but it would seem the same ratio would be useful in a CO2 spud gun, in which the volumetric advantage of CO2 over air could be taken.

Air Gun Trivia: As far back as 1800, serious air guns were used militarily. History has it that the American Lewis & Clark Expedition had one or more air guns in tow. In the military versions the air chamber was a separate ball which alternately screwed to the bottom of the gun and the pressure vessel. The pressure vessel (ball shaped) was charged with a hand powered pump. The chamber (ball) was said to have enough "charge" for several shots depending upon the opening of the valve. Apparently the valve was controlled by a lever above, which resembled the frizzen of a flintlock firearm. An ordinary looking hammer (c*ck) struck the frizzen-like lever and transmitted motion to the check valve below in the chamber ball.

Bob Swinney

I've almost decided to buy a couple of extinguishers. This project has the potential to be really cool.

Another interesting question is the ideal barrel length? Too short and you'll lose pressure before the accelerating force equals the friction. Too long and falling pressure will cause the accelerating force to fall below the friction, and deceleration will begin unless you keep feeding it carbon dioxide.

What other factors affect the ideal barrel length, I wonder?

Best wishes,

Chris

Check out the paint ballers . They have an air system for top end guns . Less pressure then the CO2 set ups but more accuracy . I think you could go with - fire extinguisher - regulator - empty tank - dump valve - spud gun . I think this would give a fair amount of consistency . Luck Ken Cutt

Not a clue as to how many shots. I only did as many shots as I needed to do. But there was no noticeable difference in how heavy the cylinder seemed to weigh.

Dan