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What psi should I use?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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What psi should I use?

Unread postAuthor: Zen/// » Sat Oct 27, 2007 4:01 pm

For a 6mm airsoft sniper rifle.

i have the stock, scope, scope mount, and bipod, all from a telescope kit.
For some reason it's perfect for a sniper rifle type design.

Here in canada everything that can go over 500fps is a firearm, Can u calculate how much psi i can have for a 450fps rifle?

oh and if u guys dont have BB's u can use unpopped corn kernals as a great subsitute.

Merged double post by MrCrowley:

Is this site dead?
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Unread postAuthor: MrCrowley » Sat Oct 27, 2007 4:33 pm

We need specs:

Valve
Chamber diameter and length
Barrel diameter and length
Pilot valve(if applicable)
Piston specs(if applicable)
Ammo weight(6mm BB's come in a few different weights)
Gun config(co-axial, inline etc)

etc I've probably missed some stuff out.


Edit:

No but your brain is.

Edit 2:

I highly recommend you do some more research before even thinking about building a Pneumatic BB 'rifle'. If you knew what you were doing you would've already given us the specs and not even needed our help with the PSI in the first place.

I'm not confident you know what you are doing, which could end up with you or someone else getting hurt.
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Last edited by MrCrowley on Sat Oct 27, 2007 4:37 pm, edited 2 times in total.
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Unread postAuthor: Zen/// » Sat Oct 27, 2007 4:37 pm

Valve: its going TO be a ball valve
Chamber diameter and length: 20cm long 6cm diameter
Barrel diameter and length: 6mm diameter 50 cm long
Pilot valve(if applicable):......?
Piston specs(if applicable).....?
Ammo weight(6mm BB's come in a few different weights).20/.25g
Gun confic(co-axial, inline etc):inline
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Unread postAuthor: ALIHISGREAT » Sat Oct 27, 2007 4:38 pm

my guess is 100-150psi but it really depends on the valve.
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Unread postAuthor: MrCrowley » Sat Oct 27, 2007 4:40 pm

It ain't gonna be much of a sniper if you are using a ball valve. When you twist the ball valve to release the air you will end up moving the gun and the BB will end up no where near where you aimed at.

Make a piston valve insetad, or a sprinkler valve should do the trick, though you will be limited to lower pressure with a sprinkler valve.

If you have no idea what a piston valve or sprinkler valve is, just search we have hundreds of topics on this forum on each valve, so just search don't ask.

6cm diameter chamber isn't necassary, with a 1" galvanized chamber 12" long, and a 6mm barrel and a co-axial piston configuration at 150psi you could get around 1000fps.
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Unread postAuthor: Zen/// » Sat Oct 27, 2007 4:53 pm

:O :o I have a commpressor and a blow gun.

Can u take a small air tank fill it up with a bike pump and hook it up directly to the blow gun and use it as a trigger?

I want it to be portable.

Imperial measurements?!?!?!?!?!?! *Head explodes*
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Unread postAuthor: DYI » Sat Oct 27, 2007 5:09 pm

Wow... I live in Canada, and we use so much imperial here that you would think we never converted to metric. You do know that in Canada, the pipe and fittings are imperial, right? And that psi is an imperial measurement?

ln my opinion, you won't be getting a metal BB anywhere near 1000 fps without either a really long barrel, or higher pressures than a bike pump can deliver, but 500 fps is easily reachable with simple short barreled designs. Just don't use a ball valve. Search "GGDT" and download the program, so that you won't need to post to ask these questions. It is easy to use, and very accurate for subsonic projectile velocities. A blowgun has horribly low flow, build a piston valve, or buy a sprinkler valve and pilot it with the blowgun. I built a large bore ball valve cannon, and even at 500 psi it needs an impractically long barrel to achieve decent performance.

And this forum isn't dead, there are a lot of us here, we just tend more towards the intelectual discussions and innovations that are posted.
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Unread postAuthor: MrCrowley » Sat Oct 27, 2007 5:12 pm

Using a blow gun as the primary valve will give you poor performance.

Just google a converter, i'm in NZ so I use Metric but it helps if you know both in this hobby.

In pipe terms these are the conversions...

1/8" = 3 or 4mm
1/4" = 6mm
3/8" = 10mm
1/2" = 15mm
3/4" = 20mm
1" = 25mm

But that's only the pipes nominal diameter.

This is going to take way too long to explain, just research it.
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Unread postAuthor: ammosmoke » Sat Oct 27, 2007 8:04 pm

Well, if the gun isn't tested, or sold commercially, how can they classify it.... :D
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Unread postAuthor: Novacastrian » Sat Oct 27, 2007 8:07 pm

I would assume that the Authorities would have to test it before they convicted you.
Doesn't make much sense limiting a gun to 500fps if they don't limit the weight of the projectile :? i.e. Limit the amount of foot pounds, like in the UK.
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Unread postAuthor: Zen/// » Sat Oct 27, 2007 8:10 pm

:) I read around and ive decided to try a spring loaded ball valve since I already have a spring, norton 180 protective eyewear and my dad, I should be fine.
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Unread postAuthor: DYI » Sat Oct 27, 2007 8:33 pm

Doesn't make much sense limiting a gun to 500fps if they don't limit the weight of the projectile


I've always been grateful for their lack of reasoning. I can fire 5 pound projectiles at 450 fps, and it's completely legal :D
(and I will soon)
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Unread postAuthor: ammosmoke » Sat Oct 27, 2007 8:34 pm

LOL, what I am saying is that they aren't going to go around looking at everybodies guns making sure they are below 500fps. There is really nothing they can do to enforce that law. Unless you run around shooting stuff with it... Then you would get in more trouble that just illegal possesion of a retarded firearm.
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Unread postAuthor: Novacastrian » Sat Oct 27, 2007 8:35 pm

DYI wrote:
Doesn't make much sense limiting a gun to 500fps if they don't limit the weight of the projectile


I've always been grateful for their lack of reasoning. I can fire 5 pound projectiles at 450 fps, and it's completely legal :D
(and I will soon)


It makes me wonder about the intellect of those in power :lol:
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Unread postAuthor: DYI » Sat Oct 27, 2007 8:43 pm

It makes me wonder about the intellect of those in power


I haven't wondered about the intellect of those in power for quite a while, I realised that there's no point pondering that which doesn't exist :lol:

5 pound projectiles at 450 fps

Well, it's actually 507 fps, but who's counting? :twisted:
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