SpudFiles

My first cannon, the combustion chamber is short 5" long, 4" dia. with a 5' long 2" barrel. I'm already planning a bigger gun, but this one has proven itself quite capable of launching a spud over 150 yds.

Welcome to the forums .

Might I say holy crap, that is one bad chamber to barrel ratio. Looks nice and clean though. Why did you make such a small chamber.
You could get better results if you shorten the barrel.

I'd chalk it up to being totally green. I had an idea of the basic construction and just whipped it together before ever looking on the web. It fires a lot better than I imagined it would given the barrel/chamber ratio, but that might be helped by the fact that my spuds are sitting probably 8" from the chamber in the barrel effectively giving me that much more chamber. I'm going to play around with some different tweaks this weekend, possibly shortening the barrel or just building a whole new gun and reusing my ignitor/endcap.

I'm also curious about the placement of the sparkers in some of the rigs I see here, they're all more or less toward the middle of the chamber, does my placement in the endcap make things better or worse in terms of the final product? My thinking was that if the flame front is starting at the back of the chamber and burning forward it'll produce the best shot. Is this wrong?

In the endcap is dangerous. If the gun is loaded and you set it down on the endcap, boom. It's also said that it weakens the endcap. Either in the middle or towards the back for the sparker, I'd put it in the middle as long as your chamber is not huge.

His ignighter is not mounted in the chamber, he has screws in the end cap. I'm guessing that where you got the ignition located just rite.