Barrel Mods
Barrel Mod 1
The first tip is to do with how the potato fits in the barrel. This setup is often called a spud cutter. A tight fit is desired to achieve maximum distance. The way to get a tighter fit is simple. When making a normal potato gun you sharpen the end of the barrel like this:
This acts as a "cookie cutter" and cuts the potato to the correct size of the barrel. The best way to do this is with a Dremel tool or a bench grinder.
What I have found is that if you sharpen the inside of the barrel like this:
you get a tighter fit. The only concern is you need to sharpen it at a very slight angle or the potato will fit in too tightly. The best way to sharpen the inside is to use a Dremel tool, or secondly to use a rounded file.
Barrel Mod 2
The second tip is used on muzzle loading barrels and is to insert a stopper into your barrel so the potato will not fall into the expansion chamber. This is very easy to do and saves you a lot of trouble in the long run. This tip doesn't apply to breach loading barrels.
First drill a small hole in your barrel as close as possible to your expansion chamber. Next you straighten out a carter key, use a bolt,or you can also use a piece of clothes hanger. The hole you drill should be slightly larger than the carter key. Place the carter key in the hole and bend over the ends. Seal the ends of the carter key with a high strength epoxy to keep the flame from escaping. Here is a picture of how it looks depending on the type of barrel you have:
Type 1-removable barrel (like green hornet)
Type 2 (other guns)
A side note: It may actually be better to use a 10-24 bolt in place of the carter key. This causes less chance of leaking.