SpudFiles

I'm only really wanting decent performance.

I have quite a lot of materials and if I dont have the right ones I can go to B&Q.

I want it to be portable but I can make it bigger.

I dont want it to be too loud because of the neighbours

I dont want to spend too much, I built it out of spare parts

I'm using an air compressor

Somewhere around 30mph?

sharpshooter11000 wrote:I'm only really wanting decent performance.

"Decent" is a bit vague. Do you want to be able to put a marble through a soft drink can? Or does it have to go through a soup tin? Or a 1" thick pine plank? I said marbles, what sort of ammunition did you have in mind?

I'm assuming you're in the UK, you might be aware that a barreled device capable of more than 12 ft/lbs of muzzle energy is considered to be an illegal firearm, ownership of which carries a mandatory 5 year prison term. I don't mean to scare you and I'm not aware of any UK member of this forum that has ever had a run in with the law, but it's good to keep this in mind.

I have quite a lot of materials and if I dont have the right ones I can go to B&Q.

Good

I want it to be portable but I can make it bigger.

Let's say a maximum length of 3 feet.

I dont want it to be too loud because of the neighbours

This means either you add a suppressor, or make it with a relatively small chamber compared to your barrel volume.

I dont want to spend too much, I built it out of spare parts

With some careful thought it doesn't have to cost an arm and a leg

I'm using an air compressor

... so unless you want to upgrade, you're stuck with 100 psi, correct?

Somewhere around 30mph?

I'll give you that, it's actually 24 mph

Yes I'm in the UK. I'd quite like to be able to fire a potato into a drink can, rather than just denting it.

Let's say a maximum length of 3 feet.

OK

This means either you add a suppressor

I was thinking of doing that.

you're stuck with 100 psi, correct?

unfortunately, yes.
Edit: I've just tried and i can get it up to just under 130

If you're willing to fork out for a QEV, with a 2 foot barrel and say 500mL chamber you should get the performance you're after comfortably at 100 psi.

It's basically the ball valve that's limiting you at this point, either keep it as it is and find a mechanical way to open it quickly and consistently, or replace it with a better valve.

If you're a bit creative, with some lateral thinking and high strength adhesive, you can make your own QEV for a fraction of the cost of a commercial model.

Here's my epoxy advice if you think it might be the route for you, generaland piston specific.

I might go for a QEV at some point but for the minute I think I'll try and come up with a mechanical valve opening thingy.

Thanks for all your help!

Good luck, here's some high speed footage courtesy of fellow englander al-xg to inspire you in the meantime

[youtube][/youtube]

Of course I have to promote my own stuff...

http://www.spudfiles.com/forums/my-thir ... 20335.html

For any pneumatic fittings this website is one of the best as it can often be hard to find pressure rated parts in b&q. They also have different sized QEV's.

http://www.airlines-pneumatics.co.uk/

Depending on the valve, chamber, pressure, barrel, etc, speeds of projectiles for simple launchers vary over a very wide range. Projectiles for most are typically in the 300-600 FPS range. Some are much slower and some are faster.

Typically, a ball valve gun shoots 317.45 fps.

Ok I had to

Thanks everyone that's been a great help