SpudFiles

I was just thinking, what if you made one of those very simple smoke bombs out of sugar and potassium nitrate. You could possible make them so that they could be thrown in the chamber of your pnematic and if you made them the right size you could fill your chamber to a specific pressure. As long as all of your smoke bombs were the exact same size. Its not really that exspensive if you were to use it on a smaller gun, but a bigger gun would probably make it not very practical. Incase any one does not know the smoke bombs do not exsplode the just make alot of smoke.
Im really not shure if this is against form rules beceause it is kind of a solid propelent, but it does not exsplode, so if you have to just delete it.

i doubt it would create enough pressure and the heat from the burning would melt your chamber anyways and you would be screwed.

they only produce a very small flame and you can hold them in you hand, not that I do though beceause ocassionaly they fall apart and burn away.
So you could just put them on tinfoil or something. If they were used in a smaller gun it would probably produce enough pressure.

yeah i guess i dont really know the pressure created. i still think the heats gunna do some damage. and it could be pretty messy. i had a friend that just mixed the kno3 and sugar dry and it burnt through a pie tin. guess it just needs to be tested.

That definately wouldnt work. The smoke bombs you are talking about actually make huge flames and can vaporize ALUMINUM. I think that aluminum vaporizes at a higher temperature than PVC or ABS. If you made it out of steel tho, it might make a cool smokey potato launch. But definately not in a plastic gun. That and you would probably have to alter the composition of the smoke bomb so it had more potassium nitrate so it would burn quickly and thus make a lot of pressure fast so it wouldnt cool down to fast and lose pressure. Probably need a different chemical mixture for the effects you want. Creative idea tho. it might warrant some further investigation...

It's like in a combustion gun...the pressure is created by heat from a combustion....if you use sugar + KNO3 to generate pressure, the pressure will rise for a few seconds and then come back to atmospheric pressure.

Here I found a site that talks about the kind of smoke bomb that I am talking about, look at the pic at the top right, you can see that there if very little flame,although there may be a large flame with a larger smoke bomb, I will do some testing though just to make shure. I will let you all know how it goes, I don't plan on testing it in a pnematic very soon though.

http://unitednuclear.com/smoke.htm

Also the thing with the flame could be over come by haveing a wide diamiter chaber and as it is burning could you not just turn the chamber so the flames are aiming toward the longer part of the barrell, it might help keep some of the heat of of the walls would it not?[/img]

I mixed KNO3 and sugar without melting them and put a small amount of this in aluminum foil, and it burned right through it. However, i got a glass orange juice bottle and put the same mixture in it and it held up. So i would suggest doing this, but then again, a bike pump is way easier than what you guys are talking about.
Edit: I just saw the pic you were talking about with the "small flame", did you notice the size of that compared to the smoke bomb in his hand? I'd bet that that particular picture was taken right before the smoke bomb was finished burning, and therefore you dont see the flame that we're all talking about.

Try the old caustic soda and aluminium foil trick,creates alot of hydrogen gas and that can be used to make a pneumatic fire supersonic rounds.But it also creates alot of heat and also dry ice but that makes the chamber cold and thus brittle but maybe it could be used in a metal holding tank.

Potassium Nitrate cost more then would be pratical, i think Alka Selzer would make more presure anyway. Mentos and Coke would make plenty of pressure, but a big mess also. I'm sure there are other combo's out there better then smoke bombs, less dangerous also.

a quart of potassium nitrate cost me 3 dollars

if it was free i still wouldnt use it. it would be a mess everytime, probably not create too much pressure in the first place, and would most likely do damage to the chamber.

baking soda and vinigar??

BLB over went over this... He estimates it would take .5 USD to fuel a standard pneumatic. So right now a hand pump is the best balance between cost and portability.

How about a foot pump?
Or attach two of them to both your feet and load as you go.