Shooting a 4lb frozen chicken at 190fps on just 25psi they

[zebra]

I would like all of you to read this relatively interesting article:

What pressure is best for a PCP?[/QUOTE]http://www.pyramydair.com/blog/2006/06/what-pressure-is-best-for-a-pcp/embed/

It talks bout what you can achieve with low pressure PCP guns. 

And why is that?

A while ago I tried to start a discussion here about why the current PCP gun air pressures need to be run so high and why we can't use the other half of our tanks - a subject that bothers me a lot... because it makes no sense.

It became immediately clear that the conversation was going to be pointless because the vast majority of the people who posted believed incorrectly, but with all their hearts, that either higher air pressure equals more power, or that a minimum pressure of more than 1000 or 1500 psi was needed to achieve acceptable power.

It's surprising how many otherwise knowledgeable people (about air guns) still think this. But it's wrong. Your air gun is capable of far more than 30 fpe or 50fpe when it drops below 1500 psi.

At the time it was too hard to explain to every single person why they were wrong but now, hopefully I can with the help of our lord... I mean our gay lord...um... I mean Tom Gaylord...

You see, 200 years ago, a PCP rifle was capable of firing a 50 cal round ball at 600 fps on just 500 psi and still got 10 shots per fill. Those rifles produced more energy than my 25 cal Cricket by a good margin but, for some reason, we're like "oh no, I've fallen off the reg and have to stop shooting" when we drop below 2000 psi.

The 35 cal Ataman rifles can barely manage 10 shots off a 4500 psi fill. We are going backwards. Fill pressures are going up, convenience is going down and we're still not making the most of our air because nobody is trying to figure out how to use the whole tank. 

My scba tank is approaching 3000 psi of air left and I'm thinking "it's time to get it filled" already. It's madness. I want to use the rest of the air I paid for! 

In 1817, guys could kill 10 deer at 100 yards on a 500 psi fill with a 50 cal air rifle. 200 years later, the 3000 psi in my scba tank is not enough to fill my 25 cal... just think how many shots we could get, in the age of regulators and 4500 psi tanks, if our air guns were designed to run at lower pressures....

That's a future topic to think about once everyone is cured. For now, just sharing an interesting article.

Enjoy! I intend to try firing a 4lb chicken from a homemade air cannon using 25 psi personally! 

 

[RollingStone]

Look up "Chicken Gun" on Wikipedia...maybe you should thaw the chicken first !!!!

 

[Saltlake58]

I think the pressure needed for a PCP is whatever it was designed for. Crosman is looking towards the 1000 to 2000 PSi guns, several 3000 psi guns that do quite nicely. Other vendors are producing 3000 PSI and higher guns, that work quite nicely.

​More pressure does not equal more power, but probably more shots per tank. The Crosman low pressure guns don't get nearly as many high power shots as the high PSI guns. If you are using a sub-12 foot pound gun, the shot counts go even higher.

​You get more, just not more power

 

[T3PRanch]

What we need is an automatic pressure adaptable valve. Possibly use chamber back pressure as a sensing element.

Walt Disney uses air cannons for their firework shows to achieve exact shell placement at desired ignition altitude.

Thurmond

 

[zebra]

"T3PRanch"What we need is an automatic pressure adaptable valve. Possibly use chamber back pressure as a sensing element.

Walt Disney uses air cannons for their firework shows to achieve exact shell placement at desired ignition altitude.

Thurmond

Now this is the sort of ideas I wanted to kick around in a discussion! 

I was thinking the same thing, or to make it easier, maybe even a dual valve design (with a switch) so you could switch over to the other one once the pressure dropped below a certain level. I.e. One valve from 3000psi down to 1500 with short opening times and another for 1500 down to 500 with longer open times. 

That custom board for the Daystate Airwolf has a similar potential with the variable force / length solenoid hammer strikes but to get the best out of it, the person setting it up needs to accept that the gun doesn't need to be refilled just because it reached 1800 psi. 

With the right programming and a determined user, I think that set up has the most potential to extend the useful pressure range because you can vary the pulse length. In real terms that means you can program it to apply more voltage at certain pressure levels and that causes the solenoid hammer to strike with more force. Then you can vary the length of time voltage is applied for. The solenoid hammer stays extended for as long as current is applied and is returned via a spring when the current is shut off.

One of the keys to the old guns delivering more power from lower pressure was apparently keeping the valve open longer for each shot. 

Btw, the big bore guns of the old days apparently got no fewer shots per fill even though they only filled to 500 psi. The 50 cal described in the article got 10 powerful shots per fill on 500 psi. The Ataman 35 cal rifle gets 10 shots (max) from a 4500 psi fill because the reg is set too high and the valve is inefficient the way it's set up.

The more shots per fill would come from being able to use a broader range of pressure. I.e. Instead of going from 3000psi to 1700psi, we might be able to go from 3000 down to 500 psi (or less) with a clever design. 

I think the first part of fixing this abomination of inefficiency and poor design is asking for guns with regulators designed to run at lower output pressures. 

I've seen diy co2 guns putting out 400fpe+ on 800 psi so I don't think we should be dropping off the reg at 1800 psi on a 22 or 25cal (or even on a 357). 

In nothing else, I want to get the most use from my scba tank. We got 4500 psi tanks to fill 3000 psi guns. Now guns fill to 4500 psi so we either need 6000 psi tanks or to reverse this trend. I have yet to see one of my guns perform well on a 300 bar fill anyway.

 

[cernunnos]

The air cutoff valve in the Huben is a flow control valve having some of the action you're looking for. (There are separate valves for initiating and cutting off the air release.) It acts a bit like a spring loaded hinged flap that can cover the transfer port. As the air flows past the stopper, the stopper is sucked down over the port. Pressure build in the barrel behind a heavier projectile will slow the flow and hold the valve open longer. 

But it seems the valve will cut off at a similar air inrush speed, not necessarily a constant projectile speed. And even if the projectile speeds were constant at shutoff, different weights will accelerate differently down the barrel. So I'd say a semi-compensating valve is possible, but matching muzzle velocities over a wide weight range ain't gonna happen.

 

[zebra]

"cernunnos"The air cutoff valve in the Huben is a flow control valve having some of the action you're looking for. (There are separate valves for initiating and cutting off the air release.) It acts a bit like a spring loaded hinged flap that can cover the transfer port. As the air flows past the stopper, the stopper is sucked down over the port. Pressure build in the barrel behind a heavier projectile will slow the flow and hold the valve open longer. 

But it seems the valve will cut off at a similar air inrush speed, not necessarily a constant projectile speed. And even if the projectile speeds were constant at shutoff, different weights will accelerate differently down the barrel. So I'd say a semi-compensating valve is possible, but matching muzzle velocities over a wide weight range ain't gonna happen.

Maybe not with the Humben design but it's possible. 

A regulator makes it possible. They just need to make guns that work on lower output pressures. If the gun works on 500 psi, then a regulator should allow consistency from 4000 psi down 500 psi. 

We need to start by breaking the myth that the reg needs to be set at 150bar to get 50fpe from a 25 cal. You could achieve 50fpe from an 800psi co2 cartridge if the flow of gas is large enough. It's all about the volume of air. 

This is where most people get stuck and find themselves dying to respond with something like " yeah but there is a minimum output pressure you need to get 50fpe". This is the myth that needs breaking. If there is a technical minimum, it's well below 1000psi or even 800 psi.