Good question!  You have a ball that you want to shoot out of the gun but which pipe will I need? 
Measure the ball and find the pipe that is just slightly larger than the ball - or slightly smaller if the ball
has a little give to it.  You want a snug fit but you don't want to have to force the ball into the barrel - after
all we don't want to make a pipe bomb, we just want to launch a ball.  Look at the chart below for PVC
pipe size information.  Lets say you have a ball that measures 1.5" diameter.  Using the chart below you
can see that the best fit for this ball would be 1-1/2" schedule 40 pipe.  The inside diameter is just slightly
larger than the ball.

…my combustion spud gun fire on the first click?

Well, as most ballistic professionals will tell you, you have to have a propellant. That is the easy part, as
most propellants come in the form of aerosols such as Axe Body Spray, Right Guard deodorant, Aqua
Net hairspray, starter fluid, and the list goes on and on. What most people don’t know is that in order to
fire, the fuel also needs oxygen. A common assumption is that the more aerosol you spray in to the
chamber the farther the ammo will go. This is not the case. You also need the correct amount of oxygen
in the chamber at the correct ratio with any form of propellant other then compressed air. Think about it.
How does a gas power engine work? How does a gun, for that matter, fire? You need the correct amount
of oxygen coupled with gunpowder to fire the gun. Fire needs oxygen.

Try this, spray less aerosol propellant into the chamber. If that does not work, after spraying the aerosol
into the chamber, blow into the chamber for about three seconds before capping. This should maximize
your range and efficiency. Remember, you need the correct fuel to oxygen ratio when firing your
combustion cannon. If more power is what you are after, then try a bigger chamber that will allow for a
greater ratio.

If you are having trouble with the second or third time you fire your cannon, then you have a “gas problem”
Yes, that’s right, you have a “gas problem” that Tums or Rolaids cannot fix. Gas it what propels your
ammo through the air, and is created when the fuel and oxygen are ignited. Try blowing into the chamber
to clear the remaining gases trapped inside your cannon. You may want to think about a small fan that
runs on batteries that is mounted inside your chamber. However, I’ll save that for another time.

If you have tried all of these helpful hints and your gun still does not work, email us on the Contact Us
section of the site with specific details of what you are doing and what your gun’s symptoms are. We will
be glad to offer any insight to your specific issues. Who knows, we may even post your problem, and our
answer on our site.

Some Helpful Questions regarding your Sparker from "Spud Talk"

…find more information on spud guns?