Rifle recoil energy?

[FoghornLeghorn]

Purely subjective question, but pertains to rifle recoil in foot pounds of energy.

Let's say we're talking about 30-06 caliber that produces 20 ft pounds of energy of recoil.

If the test rifle is a bolt action, the recoil energy is 20 fps.

If the test rifle is a Browning semi automatic, the cycling action actually absorbs some of those foot pounds? Or is it merely a perceived phenomenon?

I had physics in college, but it interfered with my hunting and fishing, and I only got a 'C.' I musta been fishing when we studied the above.

[tangolima]

If the rifles have same weight and MV, the recoil energy is the same.

Semi auto actions have different working principles. Gas operated actions produce lower MV as chamber pressure is lowered once the bullet passes the gas port. Other actions have little or no effect on MV. Auto loaders tend to be heavier. All this creates impression of lower recoil.

However, auto actions sometimes produce worse, not necessarily heavier, perceived recoil, because of the backward motion of the moving parts. The heavier the moving parts, the worse the situation would be. Brown A5 auto shotgun, a long recoil action, is known to be difficult for new shooters.

-TL

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[44 AMP]

It is a perceived thing. The actual amount of energy is what is produced by the round being fired. That's ALL the energy there is to work with. The recoil energy of the rifle is that amount factored with the weight of the rifle.

Its a straight math computation.

The recoil you FEEL is a different matter. Felt recoil includes more variables, than just the round and the weight of the gun. It includes TIME and the fit of the gun to the shooter.

The moving parts of a semi auto do not change the amount of energy but they do change the rate you FEEL that energy.

A stock that doesn't fit right, too long too short, too much drop, etc., doesn't change the recoil energy, it changes the way you feel that energy.

Two guns of identical weight, firing identical ammo will have identical recoil energy numbers, but can feel drastically different in recoil due to stock design and fit.

[jmr40]

With a gas operated semi-auto or full auto you get the same recoil as a fixed breach gun. BUT...the recoil is spread out over more time, and it feels like it is less. It is only a tiny fraction of a second different, but enough to make a real difference in what you feel.

A recoil pad does the same thing. The recoil is still the same, but the pad spreads it out over more time, and it is more comfortable.

Inertia operated semi-auto don't slow down recoil and recoil from those guns are a little harsher than gas operated guns.

This isn't usually noted with rifles. There are very few semi-auto rifles in cartridges with enough recoil to be even noticed. Most are AR type rifles in 5.56 which has virtually no recoil anyway.

But this is something discussed constantly among shotgun shooters. Gas guns like Remington and Beretta are noticeably more comfortable for high volume shooters involved in clays games.

You almost never see anyone using a Benelli or other inertia operated gun for the shotgun shooting sports. But an awful lot of hunters prefer the lighter, more reliable inertia operation for their uses.

The difference with rifles, and shotgun hunters is that are only a few rounds are shot each day. But a lot of clays shooters will go through 300-500 rounds in a day's shooting. The difference in accumulated recoil at the end of a day adds up.

[GeauxTide]

For me, the missing piece is recoil Velocity. My 788 in 308 is 7.5# scoped. Stock is a hollow Ramline, so I have to tighten that puppy up to keep the scope off my forehead. My 280 and 30-06 are 8.5# scoped. We don't have long sessions at the bench, either.

[JohnKSa]

Originally Posted by jmr40

With a gas operated semi-auto or full auto you get the same recoil as a fixed breach gun. BUT...the recoil is spread out over more time, and it feels like it is less. It is only a tiny fraction of a second different, but enough to make a real difference in what you feel.

Winner!

Force applied = kinetic energy / distance over which the energy is dissipated.

Force applied = momentum / time over which the momentum is dissipated.

Increase the time or distance it takes to dissipate the momentum/energy and the amount of force applied to your shoulder is reduced.

[44 AMP]

We don't have long sessions at the bench, either.

Bench shooting, as usually done, is about the worst way to shoot anything that recoils in double digits of ft/lbs. All the bench does is give you a nice flat stable spot to put your stuff on.

Then you have to sit and lean over forward, even after raising the rifle up on sandbags. Sure, its a very stable way to shoot, you get good accuracy from that, but it amplifies FELT recoil.

IF you're shooting something where the FELT recoil enters your personal tolerance range of uncomfortable (at the low end) to painful (at the high end) shooting from the usual benchrest, can be a miserable experience.

Keith, and many others advocated the "standing benchrest" for shooting heavy recoiling rifles. Shooting off the taller standing bench, your torso is essentially upright, allowing you to freely move with the force of the recoil, reducing the amount of punishment you feel.

If you don't think that matters, I suggest a small experiment. Take your rifle and shoot it from any field position, where your torso has some "give" to move under the recoil, and note the feel of the recoil.

Now, shoot it from a position where your back is solidly pressed against an immovable object. Wall, post, tree trunk, something where you have no give, and note the feel of the recoil.

I'd recommend you only do this with a rifle of light to moderate recoil. Doing it with a heavy recoiling rifle WILL be PAINFUL and could result in physical injury!!

[tangolima]

Bench shooting is actually not that bad. You don't have to lean forward much. Your upper torso is still mostly upright and quite springy, very similar to sitting field position.

I found eliminating / reducing muzzle rise during recoil makes things comfortable. Preloading bipods is my method.

Muzzle brakes help of course. Now almost every gun has one, even .223.

I think we have gone way beyond op's original questions.

-TL

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[Jim Watson]

Recoil is a momentum balance Mass x Velocity; gun momentum thisaway equals bullet momentum thataway, because it is a vector quantity and must always balance out.

Recoil energy is based on gun velocity which can be back calculated from momentum at the usual kinetic energy formula E = 1/2 MV^2.

So if you slow down the gun with gas operated internal monkey motion, the recoil energy goes down, even though the momentum does not.

Of course you could just add weight. An extreme case, but quite possible with a pistol, double the weight, halve the velocity, get a quarter the recoil energy.

The old figure of merit was gun velocity, they did not bother to figure out the energy. Too high a velocity was said to aggravate "gun headache."

[JohnKSa]

So if you slow down the gun with gas operated internal monkey motion, the recoil energy goes down, even though the momentum does not.

It's impossible to change recoil velocity without changing both energy and momentum.

If you reduce the recoil velocity of the gun, then you reduce both energy and momentum. Energy is reduced more than momentum, because it depends on velocity squared while momentum depends only on velocity, but they both are functions of velocity and therefore changing velocity changes both of them.

[tangolima]

The gun's moment is the same as the bullet, which is constant. Add weight to gun and its velocity will reduce (same momentum). Its energy however will reduce. Momentum unchanged and energy is different.

Can't do it with auto action moving parts though.

Auto loaders, especially gas guns, tend to recoil milder. The gas port does lower bullet's MV, and the more complex action adds weight.

-TL

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[Shane Tuttle]

I'm not exactly a physics expert. But I have to be in the minority, here. I believe there is less energy in a semi-automatic than a bolt action if measured at the butt of the firearm.

Is it noticeable by the shooter in a practical sense? I don't think so. I believe the measurement is imperceptible. However, on a technical scale (a tiny one, at that), it's less. I would think the recoil spring changes a portion of the energy's path and not all of the initial force fully transfers through it.

One thing's for sure, I could very well be wrong.

[Jim Watson]

I think what we need to do is to put a gas operated rifle in a ballistic pendulum and shoot it with the gas port open and closed. Look for a difference in swing and speed of swing.

[44 AMP]

I believe there is less energy in a semi-automatic than a bolt action if measured at the butt of the firearm.

You would be right if you just measured the rearward velocity of the firearm. But, its got nothing to do with idea of the semi auto absorbing energy because its a semi auto, it has to do with the fact that to make a semi auto you need more parts, therefore more weight (mass) that is being moved by the recoil energy of the fired round.

Remember that in semi autos, the bullet has left the barrel before the action unlocks and moves, and at that point no more energy is, or can be added to the system.

IN order to make a fair comparison using the rearward velocity of the gun to calculate the energy, you need guns of equal weight. In the usual centerfire configurations, as bolt action will be lighter than a semi auto in the same caliber.

I think what we need to do is to put a gas operated rifle in a ballistic pendulum and shoot it with the gas port open and closed. Look for a difference in swing and speed of swing.

This would be the easiest and simplest way to show the difference. The M1A would be a perfect choice because you can shut the gas system off, and the rifle weight remains the same.

If very simple terms, a push and a slap can have identical amounts of calculated energy. Even though the energy is the same, the slap FEELS harder, because the push delivers the energy over a greater duration of time.

[JohnKSa]

Add weight to gun and its velocity will reduce (same momentum). Its energy however will reduce.

Yes, that is correct. If you change the mass of the gun that creates the possibility of changing momentum and velocity independently.

I was responding in the context of the statement I quoted which didn't involve changing the mass of the gun. Here's how I should have phrased it to be completely correct:

If the mass of the gun stays constant, it is impossible to change recoil velocity without changing both energy and momentum.

If you reduce the recoil velocity of a given firearm (without actually altering the mass of the firearm), then you reduce both energy and momentum. Energy is reduced more than momentum, because it depends on velocity squared while momentum depends only on velocity, but they both are functions of velocity and therefore changing velocity changes both of them.

[tangolima]

I don't have a gas operated semi auto with shut-off type adjustable gas block. But I can run the scenario on GRT with gas port feature.

It is an AR in 6.5cm grendel, 24" barrel with gas port at 14", 0.09" diameter. With gas port, MV 2823fps. Without gas port, MV 2945fps. The gas port drops the pressure by about 5000psi for last 10" of the bullet acceleration.

BTW the measured MV is quite close to the simulation result.

-TL

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[Shane Tuttle]

Originally Posted by 44AMP

You would be right if you just measured the rearward velocity of the firearm. But, its got nothing to do with idea of the semi auto absorbing energy because its a semi auto, it has to do with the fact that to make a semi auto you need more parts, therefore more weight (mass) that is being moved by the recoil energy of the fired round.

Remember that in semi autos, the bullet has left the barrel before the action unlocks and moves, and at that point no more energy is, or can be added to the system.

IN order to make a fair comparison using the rearward velocity of the gun to calculate the energy, you need guns of equal weight. In the usual centerfire configurations, as bolt action will be lighter than a semi auto in the same caliber.

I would clarify that if each firearm was of equal mass.

[44 AMP]

I would clarify that if each firearm was of equal mass.

My understanding has always been that, in Earth's gravity, mass and weight amount to the same thing. GO into space or on a different planet, mass remains constant, weight changes with the gravity.

It is an AR in 6.5cm grendel, 24" barrel with gas port at 14", 0.09" diameter. With gas port, MV 2823fps. Without gas port, MV 2945fps. The gas port drops the pressure by about 5000psi for last 10" of the bullet acceleration.

What does your program say about different cartridges/loads and rifles where the gas port isn't in the middle of the barrel but 6" or 2" from the muzzle?? For example, an M1A/M14 or an M1 Garand??

Not doubting your results, just wondering how well that applies to other guns...

[tangolima]

I will re-run the sim when I get home. For sure the difference in MV will be less when the gas port is closer to the muzzle. The difference will be close to zero if the gas port is beyond the muzzle as in m1's initial prototype.

Here the gas port is considered as a vent to the atmosphere. In real rifle it is not quite so. The reduction in MV will be slightly less. My Chrono results seem to correlate with that.

-TL

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[tangolima]

Did a few sims for different gas port locations

14" (10" from muzzle) MV 2823fps
18" (6" from muzzle) MV 2881fps
20" (4" from muzzle) MV 2906fps
23" (1" from muzzle) MV 2940fps
24" (0" from muzzle) MV 2945fps

It sorta reminds me of loading for Nagant revolver. Gun experts said no significant difference between gas sealed brass and non-gas sealed brass. I did both. The MV difference is as much as 20%. Here the difference is about 4%. But I bet it makes quite a bit of difference in recoil.

-TL

[Colorado Redneck]

I have an old Monkey Wards double bbl 12 gage. Heavy old brute. I shot hundreds of rounds dove hunting, shooting trap, pheasant hunting with that gun. 2 3/4 inch magnum number 4 buck for goose hunting was brutal. A guy I knew had a 12 gage Browning semi auto. He let me use it on a pheasant hunt. It was downright fun to shoot. Another acquaintance had a 10 gage semi auto (don't know the brand) he used to hunt Canadian geese. He let me shoot it with a full house goose load. It was very mild recoil. I know shotguns are different than centerfire, but those experiences convinced me a semiautomatic generates less felt recoil.

[FoghornLeghorn]

Originally Posted by Colorado Redneck

I know shotguns are different than centerfire, but those experiences convinced me a semiautomatic generates less felt recoil.

Pretty much my identical perception hence, the question.

And, thanks to all who responded.

[44 AMP]

Another acquaintance had a 10 gage semi auto (don't know the brand) he used to hunt Canadian geese

The only 10ga semi auto I'm aware of was made by Ithaca, and after they ended production, essentially the same gun was made by Remington for a few years.

[stinkeypete]

Simple physics isn't so simple- you really need calculus to speak physics. Sorry.

I have 2 shotguns that weigh exactly the same.
One is a gas operated semi-auto shooting 1 1/4 ounce load at 1200 fps with a kick-eeze pad.
Other is an over and under 20 gauge shooting 7/8 ounce load at 1200fps. Stiff rubber pad.
Both shotguns are excellent fits to my physique.

Simple physics says the recoil from the 12 gauge should be 10/7 or 1.43 MORE
But the perceived recoil from the gas operated semi auto is WILDLY, CRAZY LESS. You simply can not ignore how soft it shoots.

The gas operated semi auto delays the impulse to your shoulder over time... although it delivers more total momentum, it does it as a big SHOVE

The fixed breech 20 gauge delivers less total momentum but it does it all at once, Punching your shoulder.

Put it this way, would you rather have Duane Johnson PUSH your face as hard as he can (he's a huge strong guy with much momentum) or 100 pound woman boxer punch you (bare knuckles) in the face?

The calculus of this is that the total momentum is the area under the curve of a time dependent function but force is mass time acceleration and the acceleration is changing over time.