Spiraled groves ground into the PVC to rifle the barrel. Increase potato firing accuracy.-- slippyfist, Aug 26 2007 Rifled spud gun barrels http://www.spudtech.com/Right at the top of the webpage [baked] [Klaatu, Aug 26 2007] Google http://www.google.c...=potato+gun+rifling [Klaatu, Aug 26 2007] GREAT spud gun video http://www.youtube....watch?v=zbULgsPBX6QSet to the tune of the 1812 Overture [Klaatu, Aug 26 2007] my bad..... should have googled...-- slippyfist, Aug 26 2007 At least you know it wasn't a stupid idea since it is so widely baked...?-- Klaatu, Aug 26 2007 I can't imagine that any of those rifled spud gun barrels would work for more than a few shots before you'd have to clean all the potato shavings out of it.
If this problem exists, perhaps it could be solved by polygonal rifling.-- Guncrazy, Aug 26 2007 [Gun], no, I think that of all projectile materials, a potato would be slef-cleaning. My problem with this is based on the fact that cutting rifling into pvc will reduce the strenght and induce a "notch" that will initiate fatigue cracking and eventual failure.
Whilst most DWV pressure pipe people use for "spud" guns is rated to 1500PSI or so, you'll find that PVC is not only very brittle, but even worse, it's horribly notch-sensitive, and also tends to fracture into fairly sharp shrapnel. It's all bad. Might I suggest using an aluminium barrel? Even ABS has a better failure mode (it tends to yield, stretching instead of shattering) - although ABS is softer and won't hold the same pressure.
At the very least, buy a home fibreglassing or carbon-fibre-ing kit and strap your barrel if you're going to cut rifling into it. And give it a service life, say 100 shots.
Sorry to harp on, but I had a friend hurt quite badly by his exploding spud gun. A few simple safety precautions and he'd probably not be so embarrassed to take his shirt off at the beach...
That said, rifling is easy to cut - simply make a tap (hex is good, but square works as well) with sharpened steel cutting edges, with a follower that fits snugly down the barrel, holding the cutting tap square, and pull it through the barrel. I made an adjustable tap that I could wind the cutting edges out on, allowed me to do the rifling very, very neatly in 3 cuts. Then my mate went bang and I threw away all my kit.-- Custardguts, Aug 26 2007 random, halfbakery