Pneumatic Rifle

[niglch]

My friend and I are planning on building a pneumatic sniper rifle. We are thinking of using a 3/4" barrel with a modified sprinkler valve. I have done a lot of forum searching to gather as much info as possible (this will be my first pneumatic gun), but I still have a few things I am a bit unclear on. First of all, I do not have an air compressor and the spot I want to use the gun has no power outlets. That means I'm going to have to use some kind of pump (probably a foot pump or shock pump if I can find one). With that said, what size chamber would be feasible yet reasonably powerful? Also, what is a good C:B ratio for pneumatics (I have heard a bunch of different figures)? Hopefully, I'll also find a way to mount a scope and a have a bolt action loading system too which would be awesome, but first I need to focus on the basic design.

Thanks for the help!

[ShowNoMercy]

Have you ever thought of using a CO2 or HPA setup?

[fretmelter]

definatly look into co2 or hpa cuz u dont want to be pumping a bike pump or even a shock pump to 150 psi. in not sure on the C:B ratio i just usually guess. and besides the biggest feasable copper pipe isnt very large in diameter i think on like an inch. i havent seen anything bigger. i am also planning on a copper rifle build. and your sprinkler valve willonly handle i think 120psi. so i would use something more robust. especially when u can go much higher psi with copper. and if u plan on only going to 120 i would just use pvc (than again tht is a lot for pvc)

[bigbob12345]

The CB ratio is about 0.2:1 but a longer barrel doesnt give that much increase in performace its mainly the valve openig time and amount of flow.And I think you should get 3/4in cpvc so you can shoot paintballs.And the question about chamber size probaly 3ft of 1.25 pipe would work good.And are you planning to make this out of copper or pvc.
Im assuming pvc

[niglch]

Have you ever thought of using a CO2 or HPA setup?

Well, I'm planning on installing a schrader valve to start and going from there. A pump is what I have available now and I want to make sure I can make fairly well-performing combustion before I go crazy with fueling methods. I will look into this though.

definatly look into co2 or hpa cuz u dont want to be pumping a bike pump or even a shock pump to 150 psi . . . and if u plan on only going to 120 i would just use pvc (than again tht is a lot for pvc)

I was only planning on going up to 100psi or so and using PVC. Right now the chamber is going to be a somewhere around 14" long and 2" in diameter. My barrel will likely be around 30" long with a diameter of .75". I was trying to run some numbers through GGDT and came up with an estimated muzzle velocity of 302fps with a 24g projectile (does this sound right?). I'm not sure how accurate this is because I have no idea what the valve data is for a 3/4" Watermaster sprinkler valve, and I just used the figures for the similar 1" model. However, I honestly expected the performance to be a little better since my basic aerosol combustion shoots faster than this. Maybe some of my numbers are off.

[fretmelter]

well combustions are always ganna be more powerful pound for pound. simply do that the huge anount of preesure is only in the chamber for a slipt second. i have no experience with ggdt tho. so all that sound good to me. also 300fps is what a paint ball gun is supposed to shoot. but a lot of people crank it up.

[DYI]

Atmospheric pressure combustions (i.e. not hybrids) can produce and absolute maximum of 129 psig in the chamber post combustion, with a perfect mix and zero heat loss. This gas is hot (measured at >2000 C in a recent test), so a well built combustion with excellent metering and a fan running during ignition, which may produce 100 psi or so would likely beat a sprinkler valved pneumatic at 120 psi. However, a pneumatic at 300 psi could easily beat an equivalently sized combustion, hands down. A helium powered pneumatic at 100 psi could easily equal even a well built combustion in terms of per size performance. If unsafe construction techniques are used in the combustion (flimsy materials) it has a better chance of survival than the pneumatic, so it may win.

And please, don't make another post before you learn some proper grammar and spelling. Posts like you just made clutter the forum.

And to the OP, for a fixed chamber size and 120 psi, 0.2:1 will get you the most power available. For a fixed barrel size, increasing chamber volume will always increase performance to some extent, although the returns become negligible eventually.