In Jerry's thread regarding FPE, he and I agreed that there is something different about shooting a very powerful PCP that makes it's recoil pretty harsh.

I was wondering if it might be related to the length of time the bullet is in the gun. In other words, the reduced velocity compared to the firearm making the same or more muzzle energy.

What do you engineers and math guys know about it. Does that duration of the push make the difference. Would it be like a car just gently moving a couple inches at an imperceptible rate, and pinning you against the garage wall? You know, the whole mass Vs velocity curve.

What do you think. There's definitely something here that we are not making up.

Gary

Shall I write this one off as a complete bust then?

I would say it has a lot to do with the super heavy slugs moving more slowly out of the barrel compared to a powder burner gun plus probably the rushing air that is escaping outward after the bullet has left but the valve is still open only a fraction of a fraction of a second..lol. Giving us that slow and hard jolt rearward

Had a chance to shoot a couple of 45-70 and 50-110 Shilo Sharps last year and i likended the recoil to than of a big bore airgun. These guns were pushing something like 500 grain hardcast bullets at some rediculously slow FPS like 1200 fps or something close to that. And here we are pushing 400 or so grain bullets at 800+ fps. But the 45-70's and 50-110's recoiled like a big bore. More of a steady push rearward of the shoulder instead of the HARD PUNCH that something like the 300 win magnum would produce.

I think it has to be related to duration. The slug/air push is fast enough to "scope" one but not near the power of a big PB.

I think the issue is perception. No one expects an air gun to have ANY recoil or make anything more than a whisper. When it shoves you back and the muzzle blast hits your ears it comes as a shock to most all. This is usually recorded as a smile on the first time big bore shooters face. How many times have you seen this? It is a shock but not an unpleasant one that comes with so many firearms experiences. It looks different than the painful, shocked look of someone who is slipped a slug in with the target loads of his 12 gauge.

It's a new reality to have to respect an air gun's recoil and blast. I've never been bruised by a big bore but I have been scoped but never cut. A long day of shotgunning however, will leave a mark on my shoulder. I find the kick of the big bores satisfying while a magnum rifle or shotgun is annoyingly harsh both in recoil and blast.

Kent

Good point about the recoil Gary. I've noticed with the larger of my airguns even though the shots are balanced out to have little spread the final shot has more fealt recoil, ie it tends to push back more as apposed to being sharp. The first shot of course is opperating at a higher preasure but the valve duration is shorter and lift is less, whereas the final shot is opperating at a lower preasure with a longer duration valve with greater lift. It would I think be safe to assume that the final shot accelerates slower but makes use of more barrel length to acheive the same velocity, it is in the barrel for a greater period. Just a thought. Danny.

Having just finished off a couple of boxes of .45-70 sighting in a Marlin guide gun, I might not completely agree with Tofazu about the recoil being a "steady push"...especially with the heavy Bufflo Bore solids. That said, however, it certainly is different from the typical magnum rifle. Surprisingly my shoulder didn't suffer at all, but both of my wrists were killing me the next day, never had that happen before.

A few years back I used to shoot fairly regularly at a 600m range with a friend. He shot mostly .308 Win, and at the time I had a very pretty Remington ADL in 7mm Rem. Mag. You can get 165 grain factory ammo for both and I shot them back-to-back several times with loads of identical bullet weight. There is no question that the recoil of the 7mm was far harsher, it seemed way out of proportion given that the rifles were of almost identical weight. There is about 250 fps difference between those loads, but the muzzle energy of the 7mm is over 500 ft/lbs higher. Where I'm heading with this (slowely but unsurely) is that muzzle velocity is a big part of recoil energy, perhaps a bigger factor than just the weight of the projectile that is launched. With centerfire rifles it takes a LOT more powder burned to get increasingly smaller gains in muzzle velocity, and with the larger magnums much of that powder exits the muzzle while it's still burning unless you have a very long barrel. With the big magnum cartridges, the exiting unburned powder and the burned powder gasses can constitute a major part of the overall recoil energy, especially given that they are leaving the muzzle at very high velocity.

While I'm sure that Gary knows a few tricks about valving, I'm guessing that with airguns there is a similar effect. To get "X" percent increase in muzzle velocity, you are going to have to use up "Y" amount of reservoir pressure. As X gets past a certain "sweet spot" for a given projectile weight and design, Y starts to go WAY up. You will quickly reach the point where it takes a ridiculous amount of "extra" air through the valve to gain even a little bit more muzzle velocity. This is the reason why with any particular "class" of airgun, you can either have the highest power level, OR you can have a larger number of shots, but never both.

Admittedly, the equation with airguns is far, far more complex than with cartidge rifles. Since airgun valves are not positively controlled like a solenoid, a large number of factors go into determining how long they stay open and how much pressure gets behind a projectile in the breech. Balancing these factors is a big part of what makes the difference between a $4k Barnes and a $400 Sam Yang, and why Garys rifles can have both power AND accuracy. That and quality of build. And support. And did I mention accuracy? And, well a bunch of things, but figuring out how the valve system interacts with everything else is the key.

So, after wandering far, far afield in my speculations and observations, why DO bigbore air rifles recoil differently? Why a gentle "push" instead of a sharp kick in the shoulder? My best guess is that with Barnes rifles, Gary has carefully balanced the "lots of power / lots of shots" ratio for best efficiency, and his rifles don't waste a lot air. The other is that air rifles get the performance they do with VERY low pressure compared to cartridge rifles. As far as airguns go, 4000 psi is the edge of the universe, but the 7mm RemMag that I was talking about earlier has a SAAMI maximum pressure is 61,000 psi. It's going to be a long, long time until you see that kind of pressure available pneumatically, if ever. I'm not sure that I'd be all that comfortable having a tank sitting around with 60,000+ in it all the time. In a powder burner, that pressure is only there for a split second, and sometimes they still blow up if people do something stupid like shoot with the muzzle plugged.

Hi Sean,

Hey - first off ... I've been working on your Stainless Woodsman. Have the trigger assembly made. Laying out the tower for milling with the things in mind we changed. AND, I have the inserted valve body done. The valve and trigger block take far longer than they should - but make the gun. It's happening. ;?)

Thanks for contributing to the thread.

Now; for my experience ... I don't know where these "gentle push" guns come into the picture. That was not anything I was describing. My big guns hammer my shoulder. Nothing gentle or pushing about it. It seems pretty raw to me, and I don't think it's just that I've gone soft. What I was getting to was that ... I would NEVER put myself behind anything that was gonna hammer me ten times as hard as one of my big guns. It'd kill me. So; I still don't understand the physics ... but it's different from shooting a firearm.



Gary

recently someone tried to explain torque vs horsepower. his analogy was torque is a linebacker and hp the running back. meaning; you can have 2 cars produce the same hp but different torque and they make these figures at varied levels.not sure if this applies to what your discussing.... btw i failed math
as Herman Cain would say "apples and oranges"
steve

Hi all, I sometimes visit this forum but this is my first post. I build big-bores, mostly stainless & titanium (e.g. Neil's)

To answer the question mathematically: yes Gary there is a real quantifiable reason behind it.

Momentum, p = mass x velocity
Energy, E = 1/2 mass x (velocity)²

For a given energy a slower, heavier bullet results in higher momentum, therefore a higher change in momentum occurs.
So it doesn't matter how long it's in the barrel for or how the push is spread out, it's the bullet's total momentum change. (ignoring propellant mass)

Remember that reaction force is related to change in momentum not change in energy.
When the slug/bullet has left the gun the momentum of the two should sum to zero (conservation of momentum law).

(b = bullet, g = gun)

( m(b) x v(b) ) - ( m(g) x v(g) ) = 0 (use the minus sign if taking both as positive velocity)

You can find the free recoil velocity of the gun by dividing its momentum by its known mass. Then recombine
to get the free recoil energy (to compare to firearm charts)

Note: for the complete picture, the m(b) should be all the mass leaving the barrel, and v(b) should be its average velocity - so it includes propellant.

The additional & lesser reason why airguns have more recoil for the same power level is because a much higher mass of propellant is
used per foot-pound in airguns. In firearms, smokeless powder is converted almost entirely into gases so we can directly compare propellant mass.
E.g. a .45ACP might expell 7gr of gases while my efficient big-bore would put out 100gr and a gas guzzler would put out 200+gr of air
for the same performance.

That's why firing a centrefire rifle blank feels like nothing but blank firing a big-bore PCP can give quite a shove!

Hi Mr Clark, I'm in NZ as well. What you say makes sence. With my smaller airguns which I run at 3800psi I use a hand pump to keep the air up because there is no 4500psi service here. I've noted that the first shot off the top takes less pumps to get back up to preasure than further shots. ie the further down the shot count the more pumps per shot it takes to get back up to preasure which makes sence as it would take more air mass at a lower preasure to achieve the same valocity/energy. With that being the case the final shots at the same velocity contribute more air mass to the over all equasion. Danny.

Welcome to the forum. Thanks for the post.

I won't claim to have followed more than the general outline! That was pretty thorough
You were clearly paying attention in math class. Thanks for the explanation. So; I'm not nuts after all. It is a kick in the pants.

Glad to have you.

Gary

I knew it was real and sooner or later the math would come out! Thanks for the clear presentation of the physics. That could be the best first post ever.

I'm glad the input was useful. Good to have another NZ'er Danny, I saw your posts about helium and CO2. Let's hope these big guns remain low profile specialist tools and we don't have an incident.

More air usage at lower pressure makes sense, efficiency tends to decrease with decreasing pressure.

Another way of looking at the recoil is: the closer the projectile & gun's mass are to each other, the closer their velocities will be,
therefore the closer the recoil energy is to the muzzle energy. More FPE punishing the shoulder.

Ahhh, the creator of Neil's Clark Arms 50 caliber . . . awesome gun. Really glad you signed on and posted . . . thanks for the explanation and we hope you'll stick around!

-- Jim

That was a great explanation

Gotta go to sleep now to let my brain rest from all that scientific info..........lol.

Seriously......thanx for posting that