Wow. I'm really liking these hybrids that are starting to pop up. I came up with a design last year with a lot of similar ideas but haven't had the time or money to build. This certainly serves as good inspiration to give it a shot. Are you planning to put some sort of pressure relief valve behind t...

I think it is smartest to use an air spring for this. I have never actually built one, but by adjusting the pressure behind the piston you could fine-tune the strength of the "spring" to open at a desired burst pressure. But I guess if you have a strong enough spring then go for it. Also, once the p...

The muzzle break really changes the sound of the gun and gives it that high-pitched character. Without it, you get more of a loud pop. In case anyone is curious, the barrel was rifled using a long wooden dowel with 4 wood screws in it. It was driven through the inside of the barrel with a hammer and...

I made this under-over advanced combustion cannon with a friend last summer. It performs very well with an HGDT estimated muzzle velocity of over 500 ft/s with a 70g projectile. It's got quite a kick. The only drawback to the gun is its heaviness. The fuel and metering system strapped on board adds ...

This pneumatic rifle uses a 2" piston valve actuated by a 1/4" ball valve as a firing mechanism. The piston itself is made from a 1.5" PVC cap filled with epoxy with the rubber sealing face sitting inside. Sidewalk chalk and wooden dowels are the primary ammo. The gun was finished in July of 2008 an...

Well I'm home for the week without much to do so the only logical course of action was to start drawing designs for a hybrid piston valve. Of course I have no idea if I'll actually be able to build this any time soon since it looks like I'm going to be away from home during the most of the summer. A...

Wait a minute, by fuel cell do you mean some sort of electrolysis apparatus? Hydrogen fuel cells react hydrogen with oxygen to produce an electric current. The byproduct is water and hydrogen is consumed rather than produced. An electrolysis apparatus effectively does the reverse of this process and...

Here are some things I have thought about: Define a custom fuel by specifying its properties (heat and rate of combustion and whatever else is relevant in the model). This could work for people who want to see how some weird fuel would work (like hydrogen, methane, etc.) in their design. A way to co...

As long as you use pressure rated pipe you should be fine. It's not really a safety consideration, but I would recommend an off-board meter if you don't want a heavy gun. You also might want to try to find yourself a cheap 1/4" or 1/8" NPT thread tap for your meter to chamber connection. It's not to...

8 gaps could probably be considered a little over the top for most cannons. However, I have gotten 2 gaps working pretty consistently in my old aerosol cannons with a regular piezo BBQ igniter. You just need to make the spark gaps small enough (they don't need to be very big anyway to do their job)....

I just found an interesting post on slashdot. Apparently, a company has developed an air cannon that fires wire/netting from a ship in order to deter pirate vessels. The netting spreads across the water where it can entangle in the propellers of pirate boats thus allowing the vessel under attack to ...

Yes, but don't go trying to use it as a pneumatic AND a combustion at the same time :wink: And I doubt the burst disk would decrease performance. They are about the best way to release pressure quickly. You don't see them in a lot of (atmospheric pressure) combustions because the performance gain is...

I stand corrected. No melting. Anyway just use pressure rated PVC and you should be OK even with a burst disk.

Well the maximum pressures you're going to see with a perfectly stoicheometric (1x) mix of butane/air is probably about 90-100psi in a sealed chamber. These are pressures that PVC can handle provided you are using pressure rated fittings and pipe. Therefore, you probably won't blow up your cannon ev...

I've been trying to come up with ideas on how to get 3/4" OD copper or aluminum tubing (barrel) into a 1" iron or steel tee so that it extends inside and can form the seat for a piston valve. So far, the only thing that makes sense to me is to maybe use a compression adapter and get the tubing to so...