In article ,
Adam Smith wrote:

I wonder what they use in those potato and pumpkin cannons?

The only one I ever saw used a 2" iron pipe with a cap on the end tapped
for a spark plug. Some butane was sprayed into the pipe from a lighter
refill canister, which mixed with the air of course, then the potato was
jammed in almost to the bottom to compress the mix. Then, a 9V battery
was applied to an ignition coil hooked to the spark plug. Next time I
saw the potato it was hundreds of feet in the air. I didn't do this
myself BTW, and I didn't want to be anywere near it when it was
fired--I'm not crazy. I saw this experiment at an
all-engineering-students frat house back in my college days.

Bah... You make it sound like all spud-guns are an accident waiting to
happen.

Well, they are... But mainly if you can't AIM.

Best one I ever encountered was made out of nothing but PVC pipe and a
flint sparker out of an old coleman lantern. Barrel was 1.5" pipe about
3 feet long, with a fiarly long taper cut on the inside edge of the
muzzle end to make a pretty decent "knife edge" for cutting out good
tight-fitting chunks of potato. The "breech" was made out of a 4x8 inch
"cleanout" section with a screw-in cover, and the barrel was threaded
into a 4-inch to 1.5 inch cover/cap that fit the cleanout tube. Punched
through the side of the breech was the sparker. Firing sequence: Unscrew
breech plug, spray a 5-7 second shot of rite-gard, final-net hairspray,
or similar into it and slap the cap on. Grab big tater, and punch down
onto muzzle end, cutting out a tight-fitting chunk of spud, punch
spud-slug down with a carefully measured chunk of broom handle for
compression, point, and spin the sparker. T-whunk! Tater gone bye-bye!
At a rather impressive rate of speed.

Worked OK for watermelon, too, although that was more of a "shotgun"
sort of ammo - The "slug" tended to break up on its way through the
barrel, and generally came out as a splatter of red pulp, closely
followed by the rind. Apples worked at least as well as potatoes.
Tomatoes didn't do so good... The one experiment with those was classed
a dismal failure - It didn't shoot the tomato - just turned it into
ketchup, with a sound not all that much unlike a half-liquid fart.

We messed with that thing on and off for the better part of a year
before one of the crew mis-aimed just enough to send the slug over the
fence to shatter against the neighbor's house - only about 10 inches to
the left of his 6x10 sliding glass door. We decided that things could be
a bit "messy" if we kept using that area asa target, and wisely moved
along to other pursuits. The guy's intended target was the fence itself,
but he aimed just a touch high, it seems. I was able to watch the
spud-slug miss the top of the fence by MAYBE 2 inches. The THWAP! as the
spud hit the vinyl siding was quite impressive. At least to us. Neighbor
was less than properly enthused. Can't really say I blame 'im...

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