The Accidental Cannon




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On and off, I've been working on an all-metal (and hence non-shattering) version of the Jam Jar Jet. My latest version was supposed to be adjustable, but it turned out to be ballistic.

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Step 1: Do It Outdoors!

When I first made this, I made it inside my shed, expecting a vertical jet of flame at most.

Instead, I had a can of burning meths ricocheting around my ears.


(Note to self - buy fire extinguisher!)

Step 2: Materials and Tools.

I used five things:
  • An empty tin of tomatoes (ring-pull kind).
  • An empty can of coke. I only ever drink the full-sugar caffein-riddled version, but I don't think it's vital to the efficiency of the projectile...
  • My Instructables Leatherman. It's a well-used tool already. I even use it to open the shed since the door handle disintegrated (I really must get round to fixing that).
  • Matches. Long ones. You'll see why.

Step 3: Make It.

Use one of the pointy bits to poke a hole in the bottom of the coke can, then enlarge it to around a quarter of an inch across.

Use the pliers to rip the top out of the can. No need to be pretty, but try and avoid too many sharp ragged edges, and don't bend the can, otherwise it won't fit smoothly into the tin.

Step 4: Fuelling and Firing

Put a splash of meths in the bottom of the tin. Just a splash, it's the fumes we're after.

Drop the can into the tin - if the fit is right, the can should take a moment to slide down as air forces its way around the sides and through the small hole.

Put a finger over the hole and give it a shake to generate plenty of vapour. Watch for spills from between can and tin.

Stand the can somewhere clear and firm.

Touch a flame to the hole.


Step 5: The Aftermath

Be careful!

It will be almost invisible in daylight, but the meths will still be burning in the tin. Look for heat-haze over it, and hold your hand well above the tin to feel for rising heat. Extinguish any flame by placing any handy flat thing over the tin to exclude oxygen.

If you used too much meths, there will be some left in the coke can as well. If it landed somewhere non-flammable, use the remains of the match to stand it up and extinguish it like the tin.

If it landed somewhere flammable, pick it up by poking the match into the small hole and lifting at an angle (see, I told you to use long matches), but watch for more flames as leftover meths continues to burn.

If the can is dented, it won't fit in the can well enough to fire again, but dents can be pushed out fairly easily by hand, just watch the jagged edges.

Repeat until bored.

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    253 Discussions

    Logan Hanssen

    5 years ago

    instead of tearing the top off, use a can opener no jagged edges at all!

    1 reply

    6 years ago on Step 4

    Try ethanol alcohol or a bit of propane.


    7 years ago on Step 4

    Put a firecracker in the hole and replace the can with 5 gallon bucket and fill bucket 1 or 2 inches with water place can in light cracker and run!!!!!!! It shoots very high you should try it.

    Dream Dragon

    8 years ago on Introduction

    Mortar or Cannon?

    As a Pyrotechnician with some Medieval reenactment experience, my answer is that it's a mortar.

    A Cannon is actually only one of a variety of types of gun (see also Culverin, and Bombard), and they all fire predominantly horizontally to attack walls, gates or vertical structures. It generally has a longer barrel, we call it a barrel because the very earliest ones were made in a similar way to the wooden casks that were used to transport all kinds of loose goods, including Gun powder.

    A mortar fires mainly Vertically and is used to attack Horizontal area targets, like smashing through the roofs of buildings. Named after the "bowl" part of an early form of food processor called a Mortar and Pestle, a mortar usually has a very short barrel for it's bore.

    As a Pyrotechnician I use mortar tubes (sometimes called Guns, in the US) regularly and you definitely wouldn't want one of THOSE to auto ignite.

    2 replies
    KitemanDream Dragon

    Reply 8 years ago on Introduction

    Thanks for that - I never knew the difference before.

    I'll leave the title as "cannon", though, as I think that is a more popular search-term... ;-)


    8 years ago on Introduction

    I'm assuming the reason it launches is that the thrust of the first ignition is too much for the can to hold back. Why couldn't you JB weld the can and the tin together? Would it explode? Or are you worried about excess alcohols burning in places where they shouldn't be? I've read some of the other comments below and it seems like you could just make the hole a little bigger and avert explosion.

    2 replies

    Reply 8 years ago on Introduction

    I was experimenting.

    The pressure inside a normal jam jar jet is very low, and the most I expected the soda can to do was jiggle about a bit. I was going to try a variety of lengths of jam jar jet by wedging the soda can at various heights, but the first go caught me out.


    Reply 8 years ago on Introduction

    Sorry, I didn't realize how frenetic that sounded until you made that comment.


    Reply 8 years ago on Introduction

    That would make a bomb, which, if detonated with the proper safety measures, would be cool, but in this application, DONT DO IT.

    Mortars have the propellant contained within the shell, and it is ignited by impact with the bottom of the barrel. Cannons have to be ignited.

    Correct, that is how modern mortar shells work. However the manner of firing prior to self igniting shells was different. The difference I was referring to was that a cannon generally has a longer barrel for longer range and flatter trajectory as opposed to a mortar using a short barrel for high angle short range and more of a lob type trajectory. Either way keep up the good work man.