sharpening pvc

[mikespahn]

is sharpening more effective for breech loading potatos if you chamfer the inside, outside, or both?

[mark.f]

I usually use a long outside taper and a short, shallow inside taper.

[geniusbomberman]

a file is all i needed, but it took a while. i filed it a lot on the outside and a little on the inside.

[jor2daje]

I find a shallow outside taper like mark.f said works well because its the inside diameter you want cut the potato to. An inside chamfer would cut larger than your barrels bore making a tighter fit.

[mikespahn]

jor2daje:
that makes sense, i don't know why i didn't think of that.

geniusbomberman: no need, i run a machine shop, i can make just about any shape on anything. it's just a matter of deciding on the shape. i'll shape it on a lathe.

[gabeb123]

i do both it on the outside but then you should do a little on the inside so you get a tight fit.

[jimmy101]

A small amount of inside bevel will usually increase the performance of a combustion spud gun. The increased friction delays the start of movement of the spud by a little bit and allows the chamber to reach a higher pressure. It is kind of counter intuitive but that's generally how it works.

Edit:
HGDT is great for this type of question. A quick calc suggest an increase of about 10% in muzzle velocity comparing a very small amount of friction (as from no internal bevel on the knife) with the optimal amount of friction (from a small inner bevel). The friction force needs to be pretty large. Figure something in the vicinity of say 30 pounds of force in a 2" diameter barrel (~10PSI friction in HGDTs way of defining friction). In other words, ramming the spud home won't be easy.

[psycix]

Some inside taper makes it tighter.
However, too much inside taper will cause the spud to be mashed when inserting it into the barrel.
Don't taper it too much on the inside.

So: a little tapering on the inside, and the rest outside.

[maxa1]

yes i find it easier to get the potato when it is sharpened unless i have tendency to smash the potato

[Gun Freak]

maxa, I'm sorry, but that post was useless.

[maxa1]

i know i was just giving my opinion on to sharpen or not