New gun, need sugestions

sea donkey · Mon Jun 11, 2007 8:30 pm

This is my first attempt at building a spud gun. I have 4" x 15" chamber, a 2" x 5' barrel, and a grill igniter. I'm not sure how long to cut my barrel(C:B ratio I think), or how much fuel to put in. I've tried bug spray and starting fluid, and only got it to shoot once with bug spray. I tried all diff. amounts of starting fluid and still no shot. Please help.

NoXi · Mon Jun 11, 2007 8:43 pm

how long do u spray it in for?

spudthug · Mon Jun 11, 2007 9:20 pm

did u mount the ignitor right into the gun? if you did thats a very bad idea...its allways very very picky and the gap it probably really small...

put two screws into the gun and hook wires to the ignitor then hook the wires to the screws..

noname · Mon Jun 11, 2007 9:23 pm

Sometimes starting flud isn't vapory enough to ignite, and never use bug spray. Most bug spray has a bunch of icky solvents in it that dissolve the solvent welds in pipe, which isn't good.

sea donkey · Tue Jun 12, 2007 6:37 am

Thanks for the input. I tried all different spray times. I did put the grill ignitor in the chamber. I'll try putting screws in.

How far apart should I put the screws?

What would a good fuel be?

NoXi · Tue Jun 12, 2007 4:49 pm

the fuse should be around a 1 cm apart. Hairspray, axe, stuff like that are good fuel

paaiyan · Tue Jun 12, 2007 6:54 pm

I use static guard in my spray & pray. Works like a charm, I get around 200 yards on a good day. Of course my cannon is over 8 1/2 feet long, but you should be able to get good results.

Bubba05 · Wed Jun 13, 2007 10:15 pm

Even carby start is good fuel!!

Bubba

Scotty · Thu Jun 14, 2007 10:10 pm

If you use Propane as fuel the percentage sholud be 4-7% of the total volume of your chamber ( If your chamber is 1000ml you need to use 40-70cc of fuel) Your c:b ratio should be around 1-0.7 (Chamber 1000ml Barrel 700ml) To find your volume the formula is 3.1416xRadius squaredxlength of chamber ie. 3.1416x2580.64x381=3088ml .
You would need to use a barrel with a capacity of approx 2161ml or approx 3 feet long if you use the 2inch stuff ( you should cut your chamber in half is my humble opinion) that way you only need 1 1/2 feet of barrel. You will need to use around 150cc of fuel the way the chamber is now.
Peace
Scotty