The limiting factor

[Stubbers]

Law of diminishing returns - more air pressure more engineering, more expensive materials and more liability for the manufacturers and consumers. Then there’s more noise

I am sure this law applies somewhere with most things, but I am not 100% sure its been determined where that point is with compressed air.

At equal power, higher pressures allow you to in turn run less dwell resulting in reduced muzzle noise, for instance when unregulated, your 860 fps shot at 3000 psi will be much quieter than the 860 fps shot at 2000 psi. However, I am sure your statement has truth to it somewhere along the line, I just don't feel it's written in stone as of yet as to where that line is.

I think the biggest issue with increasing pressure is actuating the valve, but with technology like 'balanced valves' and pilot valves, that isn't as much of a hindrance. Heck at 4,500 psi my pilot valve sees 50 lbs of force holding the pilot valve shut, where as a conventional valve would see 350-400 lbs of holding force, which would be a pain to crack.

Then you have closing force acting on the valve, but that also can be mitigated by valve stem diameters, standard .125" valve stems would see 55 lbs at 4,500 psi, where a .061" stem would see 13.2 lbs, which is far less than the closing force of a .125" at nominal 2,000 psi which is 24.5 lbs.

So ultimately, many variables come into play and I am not bright enough to say where exactly the real diminishing return applies with pressure increase within compressed air.

-Matt

 

[LayeredOgre]

From https://www.researchgate.net/publication/326191398_Internal_Ballistics_of_PCP_Airguns

OP, if you wanna hurt your brain, give this article a read. Lol


View attachment 493613

That’s some fascinating stuff! I’m EE so not exactly my specific department but it’s always neat to learn the “why” of why things are, down to the nitty gritty and not just a cursory understanding.

 

[3Crows]

Could be for some its their rate of energy decay ballistically (primarily with pellets) which makes them more friendly for certain environments.

That is 90% of it for me right there. And that I can moderate the muzzle report is perhaps the other 10%.

 

[Chukar60]

Years back Savage Arms came out with a muzzle loader that used smokeless powder for a propellant.
It was supposed to be the end all do all of muzzle loaders.
There is a limit to what proponents of low power projectile launchers will tolerate. Muzzle loader folks never took up the Savage smokeless front stuffer, huge caliber and power handguns make up a very small portion of the handgun market. I don’t see super powered air guns becoming a large segment of the market either.
There will always be the folks enamored with higher speeds, more FPE and heavier projectiles etc.
Most of us will not go down the 7000 psi road. More trouble for most of us than it is worth.

 

[Stubbers]

Years back Savage Arms came out with a muzzle loader that used smokeless powder for a propellant.
It was supposed to be the end all do all of muzzle loaders.
There is a limit to what proponents of low power projectile launchers will tolerate. Muzzle loader folks never took up the Savage smokeless front stuffer, huge caliber and power handguns make up a very small portion of the handgun market. I don’t see super powered air guns becoming a large segment of the market either.
There will always be the folks enamored with higher speeds, more FPE and heavier projectiles etc.
Most of us will not go down the 7000 psi road. More trouble for most of us than it is worth.

Huben GK1 would like to have a word with you. While not 7500 psi, it is a 4500 psi hand canon producing gobs of power and it grabbed a huge market share in short time.

So, probably too soon to speak on what happens if 7000 psi+ compressors become normalized which would make 4,500 psi fills or regulator set points more feasible.

-Matt

 

[airgunmike56]

I am sure a lot of people are scratching three heads , You need a long barrel for big FPS power... Now comes along the little Huben pistol and its making BIG power Big FPS with a short barrel, Have we been lied too or did Huben rewrite the PCP rules??? I have both the Huben rifle and the pistol and the power these guns can make has me scratching my head,, WOW.
Mike

 

[Just Zack 2]

I am sure a lot of people are scratching three heads , You need a long barrel for big FPS power... Now comes along the little Huben pistol and its making BIG power Big FPS with a short barrel, Have we been lied too or did Huben rewrite the PCP rules??? I have both the Huben rifle and the pistol and the power these guns can make has me scratching my head,, WOW.
Mike

I'm not too awfully familiar with the Huben pistol... Seems it and the AF Texan need to have a baby though.

 

[beerthief]

"This is America ! If it is worth doing -It is worth doing to excess!"

 

[rcs9250]

Political/NFA discussion removed.******.

 

[JimD]

I think airgun pressures are inching upward. I do not believe there is one limiting factor. Compressors clearly have limits that will have to change to continue to move up. I suspect gun clearances will have to change and materials may change, at least at the high end. Aluminum is light but not terribly strong. Titanium is much more expensive but also very corrosion resistant, and light for it's strength. The moisture possibility in the air and the susceptible to oxidation degradation probably rules out carbon steel but something like 316 stainless might make sense. My point is just that many things would have to be at least tweaked to go much further on pressure. The changes might be bigger. Simplest would be higher grades and heat treatments in aluminum. The maximums get fairly close to steel (at least in steels lower grades).

But I also wonder about the forcing function. I've been chasing 50 fpe on my P35-25 without a great reason. So I am not claiming to be immune. But I really think that 20-35 fpe airguns are the "sweet spot" and will always have a market. In 177 and 22 that gives you enough thrust to shoot heavy for caliber pellets 800-900 fps. While a little faster works with some pellets at least some of the time I think 800-900 is a pretty darn good place to be in velocity. You don't need any more than 35 fpe for target shooting to at least 50 yards. You also do not need more fpe for small game hunting. Bigger animals really need more to take cleanly IMHO but how much of the time are they our target and how many guns do we need for those opportunities?

If I lived in a more arid environment where trees are much more rare and shot at ground squirrels rather than tree squirrels I might want a bit more for longer shots. I would also need to get more serious about slugs. I am ambivalent now. I don't need them for 50 yard max shooting. I also know that bullets work in firearms due to that massive jolt of pressure which makes the bullet expand out and hug the rifling. We don't have that in airguns so sealing a slug in an airgun seems to require very careful diameter control and matching the projectile to the barrel. Inherently the more we use slugs the more we are going to want higher pressures. It would help them seal, they are not limited to 800-900 fps velocity, and they work better at long ranges where more power would be at least very helpful.

†**********
Political/NFA discussion removed

 

[3Crows]

Pellets are ballistically inefficient losing energy rapidly limiting effective range and soft lead pellets tend to not ricochet with as much energy retained as a conventional lead bullet. The limit is the diablo pellet, stable velocity and energy retention. Once we go to slugs those constraints imposed by a diablo pellet are gone. There is no point in me driving a 34 grains pellet any faster than 900 fps +/- as accuracy deteriorates. If there were heavier pellets, okay. But at some point the only way to get more energy that can be used in a practical sense is to drop the diablo shape and go to a bullet shape and the velocity cap is gone.

I need to move further out. In fact, I would really like my own island or better yet my own planet.

 

[Stubbers]

Also, o-ring tolerances become much tighter the higher in pressure we go, as we have to contain our pressure indefinitely opposed to firearms that do not rely on such o-rings. The durometer is also critical. THAT, imo, is ONE limiting factor...so until 100 or 120 durometer o-rings are commercialized, we're stuck with...

As you can see, 90 duro can handle 7000~ psi just fine with nominal tolerances, so as to what the limits may be, currently on 90 duro, you're looking at maybe 9000~ psi, which is what the AEA compressor CAN push towards, while being software limited to 7,500 psi.

Material wise...titanium and or carbon fiber reinforced titanium would work great. Carbon fiber is really strong while in tension, meaning it's great at keeping compressed air inside from escaping out, while not so much keeping compression out, from escaping in (No reminder needed here with such catastrophes as the the Titan), which is in compression.

-Matt

 

[Just Zack 2]

Not sure about “maxed out by Bernoulli’s Law”, but we do work under Boyle’s Law which is still just an approximation at the relatively low pressures that airguns use, where air behaves much like an ideal gas. But once we get much above 3000psi, air becomes less “ideal”. So we are close to “maxed out” with Boyle’s Law.

Are you contemplating use of 6000psi? 10,000psi? Air is way past being an ideal gas at those pressures. For an accurate assessment at those pressures, Van der Waals equation is used (or data from actual measurements). The pressure now rises fast without packing much more air. So there is much less energy available than predicted by Boyle’s Law. And you still have the requirement for proportionally thicker/stronger air tanks in the airgun. So a lot of extra weight, with very little benefit. Shot count will suffer greatly. You can use the higher pressures, but be aware of the drawbacks. 4500psi is kind of a standard currently, so I’d keep the pressure at 4500psi and use a bigger air tank and longer barrel.

Regardless of which way you go, there is still the fact that room temperature air is very dense, so it will not be able to accelerate as fast as the gases in a firearm, regardless of pressure.

Mass flow limiting... Beyond my paygrade.

Aside from bigger tank and longer barrel, if folks want "more" going up in caliber seems the next logical step, if keeping with hpa.

 

[Scotchmo]

Mass flow limiting... Beyond my paygrade.

Aside from bigger tank and longer barrel, if folks want "more" going up in caliber seems the next logical step, if keeping with hpa.

If just more FPE is the goal, then a bigger caliber is the easy path. It’s really just scaling up two dimensions. Air use will go up proportionally.

That’s higher FPE, but that does not in itself increase the ballistic performance of the projectile.

The basic determination of FPE at a given pressure is barrel volume. Barrel volume is area of the caliber x barrel length. Caliber is easily scaled with no diminishing returns. Barrel length has diminishing returns, but it’s what’s needed to get better performance from higher sectional density projectiles, while still working with low pressures.

Long range performance with an air gun needs high BC. But, at the low pressures and high gas density, we are still talking about subsonic projectiles. There are some firearm bullets where an airgun can match their ballistic performance. Popular subsonic firearm cartridges such as 22LR, 9mm Parabellum, 300 Blackout, 45 Colt, are good candidates. An air rifle can generally have firearm performance in the handgun calibers. It’s a stretch for an air rifle to match even subsonic rifle bullet performance. It is easy enough with something like a 22LR. But more difficult with higher sectional density projectiles. Something like the 300 Blackout with its high sectional density, would be about the limit for an air rifle.

Lower power supersonic centerfire bullets: Another firearm bullet that has proven itself for long range airguns is the 25-20, or simply the .257 caliber. Though the 25-20 is normally a low supersonic projectile, it performs well at high subsonic velocities in an airgun. Same for the 45-70.

Bottom line, with the current pressures commonly used in airguns, we can still match the performance of subsonic firearms (not supersonic). Higher air pressure won’t change that.

 

[Stubbers]

The majority of pcp's from the manufacturer all have various port diameters, and the majority of pcp users aren't the type to rip it all apart and refine these dimensions.

Port diameter shouldn't be omitted or assumed to be equal to full bore, but otherwise, very well said. @Scotchmo

The other determining factor is the distribution of speeds based on the gas used. Sure we commonly use the air available in our atmosphere, but, there are those that opt for helium. Below is a GREAT visualization of how impactful the gas being used to propel our projectiles is....

Familiarize yourself with the Maxwell-Boltzmann distribution.

Likewise Temperature of gas...

Really, its a deep rabbit hole that very few dare to go. Sure the above doesn't apply to 99% of airgunners, but it still applies to thermodynamics and limiting factors.

-Matt

 

[Treefrog]

It is posts like that ^ that make me happy to stick with co2.

That said, this is a really interesting look 'under the hood' of how these wonderful things work.

Cheers,

J~

 

[Stubbers]

Yea, putting barrel volume before mass flow rate or other thermodynamic properties is putting the cart before the horse, so to speak.

-Matt

 

[Scotchmo]

Yea, putting barrel volume before mass flow rate or other thermodynamic properties is putting the cart before the horse, so to speak.

-Matt

Yes, barrel volume is the final piece, after providing for sufficient mass flow rate.

 

[LayeredOgre]

The majority of pcp's from the manufacturer all have various port diameters, and the majority of pcp users aren't the type to rip it all apart and refine these dimensions.

Port diameter shouldn't be omitted or assumed to be equal to full bore, but otherwise, very well said. @Scotchmo

The other determining factor is the distribution of speeds based on the gas used. Sure we commonly use the air available in our atmosphere, but, there are those that opt for helium. Below is a GREAT visualization of how impactful the gas being used to propel our projectiles is....

Familiarize yourself with the Maxwell-Boltzmann distribution.

View attachment 493794
View attachment 493799

Likewise Temperature of gas...

View attachment 493796

Really, its a deep rabbit hole that very few dare to go. Sure the above doesn't apply to 99% of airgunners, but it still applies to thermodynamics and limiting factors.

-Matt

Now I’m getting chem2 flashbacks haha!

Here’s a question I have, so room temp is like 300K if I’m remembering right. If you had air at say 500k, or any higher temp I guess, how much faster velocities(the projectile not the air) could be achieved? Never mind the magical heat resistant orings, springs, and plastic parts needed!

 

[Stubbers]

Now I’m getting chem2 flashbacks haha!

Here’s a question I have, so room temp is like 300K if I’m remembering right. If you had air at say 500k, or any higher temp I guess, how much faster velocities(the projectile not the air) could be achieved? Never mind the magical heat resistant orings, springs, and plastic parts needed!

Very loaded question, depends on sectional density of your projectile. However, for practical purposes...

300k / room temp (80f) nets 1000-1100 fps at most in most calibers for most readily available off the shelf projectiles
500k would net closer to 1300-1400 fps

-Matt