SpudFiles

I am wanting to make a single shot, shotgun style function for the spud gun I am planning. It will have detachable barrels, likely including 2" and 2.5" barrels, along with a 3" expansion chamber. It will use propane for fuel. I would like to make a barrel/attachment for this, so I can shoot somewhat of a airsoft scatter shot out of it. I have looked into burst disks, but it seems like these only work with pneumatic style weapons. Any info/ideas/help would be greatly appreciated, as I am extremely new to this type of activity. Thanks!

I would just use one of the barrels you're already making and then some TP as wadding, it will work very well.

Alrighty, thanks!

Burst discs can be used to quite good effect in combustion spudguns, the chamber pressure has a chance to rise before the projectile starts moving, hence the projectile (with a properly "calibrated" burts disc) will be subject to greater force upon initial acceleration.

http://www.spudfiles.com/forums/search.html , is a great tool to find long lost threads on different subject matter including burst discs.

Have a look around the combustion showcase too, you should be able to get a lot of good ideas just from looking at other peeps cannons.

Next best step is to either physically draw the intended design and let us rip it to pieces (j/k), i mean help work through it with you

Welcome to Spudfiles

I truly do not have a set design yet. I only know what aspects I want the cannon to have. These include:
Propane injection system
Car ignition coil
Detachable barrels
Safe

Why do you plan on using a car ignition coil, it is probably a bit overkill for what you plan on doing IMHO. I would recommend using a BBQ piezo or a stungun circuit (probly also overkill). A bbq piezo will cost you around 10$ and can be used with multiple spark gaps if you so desire.

take aluminum foil, place bbs in it, and shap it in a ball, drop in our barrel and fire

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l l like that with the aluminum foil and fill it with bbs, it will
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i used bbq last time with same chamber, and had to click it so many times to get a good enough spark

It was either your spark gap (should be around 10mm for a single gap), your fuel mix (i take it it was a "spray and pray"), or you just had a dud piezo, you get them sometimes.