SpudFiles

So it started as a casual bet between me and my brother as to who could build the best one. Here's mine.




It's pneumatic, this is at about 60 psi.

The valve is rather clever though I say so myself. Looks like a standard ball valve eh? Not so! There is, twixt ball and barrel, the capacity to put a burst disk. One layer of foil holds about 20 psi (very ish) so a triple layer means that when the ball opens, the gun doesn't actually fire until enough air has passed through the ball to burst the disk. Which, I hope, removes the early trickle loss of air.

There is an earlier hilarious video of this system failing terrifyingly but I'm afraid I can't post it because the cameraman dropped the f bomb after soiling himself. Hence the cowering in this clip.

I thought I was looking good! Then brother Paul, who lives on a farm, sent me this



It's a piece of field artillery.

Now I'm pretty sure I can take him on accuracy. But range and hang time? I'm stuffed here arn't I. Bringing a gun to a cannon fight!

I've tripled the size of my chamber and with a better footpump I might make 70 or 80 psi, is there anything else I can do?

use steel and go hybrid!
to actually improve your cannon get a way longer barrel, chamber barrel ratio of 0.8-1 is what you should look for.

I note that you're probably in the UK, so it's best to exercise caution in the public eye as legally a barrelled device capable of more than 12 ft/lbs of muzzle energy is considered a firearm, illegal posession of which carries a hefty penalty.

Burst disc or not, the ball valve is the limiting factor.

You can consider a two stage burst disk: http://www.spudfiles.com/spud_wiki/inde ... burst_disk



A simpler idea would be something like this:



You would need an air source like a compressor (not a big investment really) to make the above practical though. Since you're just mucking around, the small delay between valve opening and disk bursting should not be significant

How does one measure muzzle energy? I didn't even think of the legal aspect! Has anyone ever been arrested for making a spudgun?!

Surely fig 2 is basically what i've already made, only the blow gun trigger is replaced by the ball valve!

Penhorse wrote:How does one measure muzzle energy?

http://en.wikipedia.org/wiki/Muzzle_energy

I didn't even think of the legal aspect! Has anyone ever been arrested for making a spudgun?!

Not to my knowledge, but if an annoying neighbour reports some nutter shooting stuff in his back garden, you can expect a visit from the plod. The point is, be careful and don't stick you neck out.

Surely fig 2 is basically what i've already made, only the blow gun trigger is replaced by the ball valve!

If I got it correctly, your burst disk is between the ball valve and the barrel. This means that the ball valve is still a restriction. What I am proposing is barrel -> burst disk -> chamber -> ball valve -> air source, which allows for much better flow independently of how quickly you open the ball valve.

Very clever. May I suggest not holding the spud gun against or close to your Johnson if you dont want to hurt it......

I was the man standing behind the other man! My Johnson is going nowhere near that thing!!

Penhorse wrote:How does one measure muzzle energy?

The easiest way is to measure the muzzle velocity with a round of known mass. The muzzle energy is (1/2)(mass)(velocity)^2. If mass is in grams and velocity is in meters/second then the result is in Joules.

Check the spud wiki for easy ways to get the muzzle velocity.