SpudFiles

just built my first spudgun and i am having some problems with blowby and partial combustion. im thinking making the barrel end pointed so the inside edge makes the spud fit smoothly. any suggestions would be much appreciated.

Okay...what do you mean by blowby? Does it mean when the potatoe leaves the barrel? Some pics of the cannon would be pretty helpfull. And shaving away the inside tip of the barrel wont do you much good. I think that your having problems with the combustion. You said you had problems with partial combustion. If you could just give a tad bit of more information to let people know what are your problems, we would be glad to help you.

konarider321 wrote:just built my first spudgun and i am having some problems with blowby and partial combustion. im thinking making the barrel end pointed so the inside edge makes the spud fit smoothly. any suggestions would be much appreciated.

Yeah that's a common performance hop up. Grind a small bevel on the inside edge of your potato cutter. That will cause the potato to cut slightly large and fit tighter in the barrel.

I assume by blowby you mean the spud isn't fitting airtight. This is more a problem with 2" barrels than 1.5" since you need a bigger spud for 2".

by partial combustion i mean not all the propellent is igniting and blowby i mean some of the blast is passing by the potato before it lanches. it is a 2" barrel btw. thanks again

ok well both problems go hand in hand my answer get bigger spuds. and yes unlike what pvcpsyco says beveling the inside edge of the barrel at the muzzle will help form a tighter seal

I recommend a chamber fan to you for faster combustion.
It really increases performance ALOT.

Did you bevel the outside of the barrel? A single outside bevel will give a good seal as long as the minimum diameter of the spud is greater than the ID of the barrel. If you can see any gaps between the spud and the barrel that'll screw up your mixture since the fuel will be leaking past the spud before the gun is fired. When fired, the gap will give significant blowby and reduce the gun's performance.

The double bevel will increase performance versus the single outer bevel but the single outer bevel should give an essentially airtight seal, assuming your spuds are big enough. It seams to me that finding spuds big enough for a 2" barrel is getting to be harder.