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Step 7Gun it
Congratulations, you are now in possession of a "Small Bertha" model small-bore potato rifle. To test fire:
Put on your eye and ear protection. Crumple up a piece of paper to a sphere that will fit snugly but not too tightly in the barrel. Load it and stoke as far down the barrel as you can. Open the bottle cap and prime with a short blast of your chosen fuel (a short blast- quarter of a second is probably too much from a normal aerosol can). Screw the lid back on, and turn the gun upside down a few times to mix the fuel. Grasp the gun firmly, holding it against your body to prevent recoil. Click the sparker and expect a very loud bang- expecting it stops you dropping the gun and flailing like a mad person when it eventually does make one.
If nothing happened, turn the gun upside down again, wait a few seconds and try again- if this doesn't work a few times your fuel mix was probably too lean, or possibly much too rich.
If there is a slow "whoof" noise with a visible flame front and the gun becomes hot, your mixture was probably too rich- use less fuel next time. This can also be caused by inadequate mixing of fuel and air- if reducing the fuel quantity results in no firing at all, try the previous quantity of fuel and rotate the gun for longer to provide more complete mixing.
If there is a sharp bang with a barely visible blue flame, your fuel mix was about right- the paper will probably go quite a long way.
Open the bottle cap with the barrel pointing straight upwards and let the combustion chamber vent for a few seconds. Put your lips to the neck and blow (as if you were blowing on a fire or hot food, not your cold hands) for a few seconds to further vent the gun. Repeat this from the muzzle. If you are going to fire again, let the gun cool for a few seconds- hot plastic is weak plastic. If you are going to leave the gun, leave it standing with the muzzle pointing upwards and the bottle cap off to let it air out.
Put on your eye and ear protection. Crumple up a piece of paper to a sphere that will fit snugly but not too tightly in the barrel. Load it and stoke as far down the barrel as you can. Open the bottle cap and prime with a short blast of your chosen fuel (a short blast- quarter of a second is probably too much from a normal aerosol can). Screw the lid back on, and turn the gun upside down a few times to mix the fuel. Grasp the gun firmly, holding it against your body to prevent recoil. Click the sparker and expect a very loud bang- expecting it stops you dropping the gun and flailing like a mad person when it eventually does make one.
If nothing happened, turn the gun upside down again, wait a few seconds and try again- if this doesn't work a few times your fuel mix was probably too lean, or possibly much too rich.
If there is a slow "whoof" noise with a visible flame front and the gun becomes hot, your mixture was probably too rich- use less fuel next time. This can also be caused by inadequate mixing of fuel and air- if reducing the fuel quantity results in no firing at all, try the previous quantity of fuel and rotate the gun for longer to provide more complete mixing.
If there is a sharp bang with a barely visible blue flame, your fuel mix was about right- the paper will probably go quite a long way.
Open the bottle cap with the barrel pointing straight upwards and let the combustion chamber vent for a few seconds. Put your lips to the neck and blow (as if you were blowing on a fire or hot food, not your cold hands) for a few seconds to further vent the gun. Repeat this from the muzzle. If you are going to fire again, let the gun cool for a few seconds- hot plastic is weak plastic. If you are going to leave the gun, leave it standing with the muzzle pointing upwards and the bottle cap off to let it air out.
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