Most variations of the gun are best left to your imagination. But
here's a few things to get your mind going:
These are just a few ideas to get your mind going. If you come up
with any useful variations to the dimensions of your gun, please
email
them to me so I can add them to this page!
Sealant comes in only a few shapes and sizes. Ok, it really doesn't have different shapes, but types do vary. Remember to buy the right sealant for your pipe. If you bought PVC, then use PVC cement (NOT CPVC cement!). If you bought ABS, then use ABS cement. There are also multi-purpose cements that work on both PVC and ABS. Since your joints are the absolute weakest spot in your gun, you need to take the most care in making them. Right next to the cement on the shelf will be pipe cleaner. If you're cheap, paint thinner or acetone will do the same job. Regardless, the joints need to be free of all dirt, oil and plastic splinters (if you sawed the pipe). When you cement the pipe together, give the joints adequate time to cure before you put any pressure on them These steps are very important! If you compromise on the joints in your gun, you're buying a ticket to the hospital.
Depending on what propellant you use, you will get varying explosions
and
therefore get a more or less powerful shot. Among the commonly
experimented with propellants are:
Hair spray, Propane, Alcohol, Butane/Carb Cleaner/Starting Fluid, Gasoline, Ether, and Oxygen.
I have ordered the above in what
I believe is least-to-greatest power.
Hair Spray
Hair spray is probably the most common propellant and it's often used by
beginners just learning about their gun. Of all of the propellants, this
one probably guarentees to be the safest. You need to use the aerosol
type of hairspray, not the pump-action. You're using the aerosol for the
propellant which is forcing the hairspray out. Some use butane,
isobutane, and propane as their propellants, for example.
Advantages: Hair spray is cheap, easy to buy and inconspicuous.
Disadvantages: It will end up gunking up the inside of your gun, so
you'll have to clean it regularly. Less powerful than other
propellants.
Propane
Propane is the next most commonly used propellant (from my understanding,
at least). It tends to give a good powerful shot without being a
dangerous propellant.
Advantages: Propane is cheap, basically safe and easily dispensed.
Disadvantages: Somewhat conspicuous, takes more propane to get a good
shot than other propellants require, and it takes a while to
dispense.
Alcohol
Denatured alcohol appears to work well as a propellant. Because I haven't
experimented with it, I cannot honestly rank its power. It has to be
gasseous to combust, the liquid is far less cooperative. Use a regular
hair spray bottle and try around 10-15 sprays into your
chamber.
Butane/Carburetor Cleaner/Starting
Fluid
Butane is a little less common, and appears to be more powerful
than propane. I have included in this section Carburetor Cleaner
and Starting Fluid, because a lot of people like to use them, and
I believe their power is equal to that of butane. They should be
easier to dispense than butane (see disadvantages below), and
won't gum up your gun (cleaner shouldn't gum things up =)
A related propellant..Model Airplane Fuel
I've been told that Model Airplane Fuel can be used and is effective, but
is costly ($10-$15/gallon) and leaves a castor oil residue behind.
I received an email from Paul Anderson, paul@geeky1.ebtech.net on this
topic:
"I was reading over your site and noticed your request for info on firing a potato gun with gasoline. It's VERY difficult to get the mixture right, also you're not really burning the liquid, you're burning the fumes. Gasoline is a powerful propellant(all I can say is it's more powerful than WD-40), it has one MAJOR downside: It eats PVC pipe for lunch:( The gasoline dissolves the PVC, so you end up finding that the end plug on your combustion chamber becomes VERY difficult to get off(i.e. you put it in finger tight, and it takes a wrench to take the thing off). I wouldn't recommend using gasoline, unless the gun is made of metal."
Ether is a very powerful propellant. I would recommend against using
it. From email on the Spudgun Mailinglist:
"I tried out starting ether this weekend in my spud gun. Very strong stuff. Very little is needed, only 1/4th second or so spray. At the fifth shot, the glue joint between the combustion chamber and the reducer separated violently. No injuries resulted, fortunately, as the combustion chamber was not pointed towards myself. The spudgun itself is reusable since none of the plastic pieces broke, just got to reglue the joint. All told, I would urge caution using ether in spud guns , even discourage its use after this weekend."
Unlike all of the above, Oxygen is not a propellant in itself. All
propellants burn IN something else. In our case, they're all burned in
oxygen. So you probably wonder how you're doing that now? Right now
you're burning the oxygen normally present in the air to burn your
propellant. The problem with air is that most of it is nitrogen, which
doesn't aid in combustion. Therefore a good portion of what's in your
combustion chamber simply can't be burned.
Oxygen is a good solution. By filling your chamber with the right
propellant/oxygen mix (which can be calculated chemically), you will
force that nasty uncombustable gas out and be able to combust more
propellant.
Oxygen, however, has downsides. I have been told that it is safe
to use with most common propellants (hair spray, butane, propane) but
beyond that the force of the explosion is possibly lethal. The
pros and cons will sum it up.
Advantages: Complete combustion results in a much more powerful shot with
the addition of oxygen.
Disadvantages: Difficult to regulate, difficult to obtain or use and
potentially very dangerous.
Well I don't know how much is to be said for projectiles. Your imagination has free reign over this category. Anything that can and will fit in your barrel is free game. Some suggestions: