Help! Copper combustion rifle.

[Urban Ninja]

Hi Im new to this site and was just wandering if you could build a combustion spudgun out of copper piping ? The chamber being 22mm and the barrel 15mm. I know that someone on this site has built the pistol version but Im really looking to build a rifle version. Do you think it could even get the projectile out of the barrel? Ive never built a proper combustion before but loads of pneumatic, so i have no idea how to make one.

[boilingleadbath]

I understand that often people have trouble getting a proper fuel mixtures in long, thin chambers. I would suspect that the same problem would present it's self with multiple chambers.

So, let's say you put a 75mm long chamber on it (which should be short enough to avoid mixture problems). This means your barrel can be (at most) 230mm long ((22mm^2 / 15mm^2) / .7 * 75mm), for a total launcher length of some 300 mm... which is pretty short.

This could be fixed by using a larger diameter chamber or a smaller diameter barrel.

[Urban Ninja]

Thanks a lot. That really helps.

[drac]

How do you plan on igniting the fuel?

[Urban Ninja]

Ill probrably use a BBQ ignitor, but do you think that a piezo out of a lighter would work? Thanks.

[Technician]

I agree with boilingleadbath as small barrels present their own problem when it comes to getting the right fuel/air mix and ignition. The smallest useful chamber fan is around 40mm so that's out, yet it would really help if you had one.

[spudshot]

small chambers are a bitch to get right, i found that out the hard way with my pocket rocket, about 1 in 10 tries would work, i've got it down to a science now, i use butane from a mini torch