Energy Ft. Lbs. relationship to Recoil and Pressure

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BondoBob

New member
Can someone explain this relationship between energy ft. lbs and recoil? I'm trying to decide on a defense load for my 357 revolvers. Critical Defense is listed as a low recoil round but has 624 ft lbs. Critical Duty is listed as more powerful and penetrating but less energy at 487 ft. lbs. How can this be? Is there an other component to this formula I'm missing like pressure? I would think the higher the ft lbs the more felt recoil in the same gun. I'm a bit recoil sensitive I guess.
 
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Because the ME (muzzle energy) increases more with velocity than bullet weight. So on paper, a lighter bullet traveling at higher speed will look much better than a heavier bullet at lower speed. But the bullet weight will be a factor in felt recoil as well as penetration, so ME on paper is not everything.

Heavier bullets will feel like more recoil, but more velocity will increase the "snap".
Weight of your gun is a factor as well, and grips that cushion can change the felt recoil considerably, as well as the way that the grip fit your hand.

Most people have a hard time when the ME gets over 300 ft. lbs in the lighter snub nose revolvers.
600 ft. pounds is in the heftier .357 mag range.

Again, don't go by the ft. pounds touted on the box, because they might be using a 6" barrel for the results and you will get about 200 lbs. less in a 2" snub as demonstrated by many youtube videos of actual chronographed tests.

But I agree with you in thinking that a 600 lb. ME load will always feel like more recoil than a 450 lb..
 
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Kinetic energy is 1/2 Mass x Velocity Squared. So a light fast bullet will show a lot of muzzle energy.
But recoil is a momentum balance; Mass x Velocity of the bullet is equalled by the Mass x Velocity of the gun back at you.
Momentum, not energy, you are NOT feeling 450 ft lbs of recoil.

Here is one of several handy dandy recoil calculators.
It shows recoil as impulse, velocity, and energy. There is debate as to which number best estimates felt recoil, you might have to do some actual shooting to get an idea.
Note that it needs a value for powder charge. If you don't wan't to pull a bullet and weigh a factory load, you can get close enough by using a typical value from reloading data.
http://www.shooterscalculator.com/recoil-calculator.php
 
BondoBob said:
Can someone explain this relationship between energy ft. lbs and recoil?
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In general, yes, more muzzle energy means more recoil. (Now someone will come along and 'correct' me with blah, blah, blah.)

BondoBob said:
Critical Defense is listed as a low recoil round but has 624 ft lbs. Critical Duty is listed as more powerful and penetrating but less energy at 450 ft. lbs.
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Where are you getting these descriptions? They don't say this about these 357 rounds on Hornady's website. And these statements are contradictory. You can't have more power but less muzzle energy because 'power' in ballistics is often defined by muzzle energy.

BondoBob said:
I'm a bit recoil sensitive I guess.
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We all are. :) Recoil sucks.
 
To make it all more complicated there is “physics recoil” and “perceived recoil”.

For every action there is an equal and opposite reaction. A bullet flys out of one end of a gun, the gun moves backwards in the opposite direction. Force is mass multiplied by acceleration, and work... okay... lots of equations and areas under curves calculus stuff.

Since the gun weighs much more than the bullet and powder, it moves backwards more slowly. Except there is a human hand gripping the gun (pistol) tightly. So there is an effect of the mass of the hand, arm, body of the human all composed with things like fit of the grip to the hand, strength of muscles, technique (does the pistol make a broad arc ending with the pistol pointed at the sky, or is the force directed straight back to the shoulder) friction (grip to hand and absorption of energy by the grip material) then there is how fast this all happens... “fast” powders getting the bullet to 1000 FPS in 2” of barrel or “slow” powders getting the same bullet to 1000 FPS but accelerating along and needing 6” of barrel To get up to speed, effects that delay energy transfers like the reciprocation of the slide and rubber grips (rubber absorbs but bounces... delays some force, materials like Sorbothane deform and turn the energy in to heat due to friction inside the chemistry of the stuff) and the bottom line is...

There is no free lunch- the more whup-@ you deliver the more it hurts your mitten.

I am of the old school when it comes to pistols- it’s always better to start with a bigger hole. If a bullet expand, a bigger one expands even bigger. If it doesn’t you still have a big hole.

Based on many years of hunting I guarantee you that for all options even remotely practical, shot placement is vastly more important than the energy of the projectile. There is no replacement for proper shot placement.

I’m also weary of marketing. Everyone always trying to invent something new in order to sell me something. If it wasn’t for the safety factor of not loading in to older firearms, you could call 9mm “.38 Special Rimless” as far as I care. .45 is always good for big holes and momentum for those who can handle the recoil. .380 you can call “9mm light” and .32 you can call “This sure is fun to shoot and no, I would not like to be standing on the wrong side of this one either.” What about .22? Call that .22 because from CB caps to .22 magnum it’s still best for shooting small game and no, you don’t want to be standing on the wrong side of it. When I was a kid my friend Steve shot his older brother Gary in the butt with a .22 CB cap as Gary was a mean big brother. Even though it only penetrated two layers of denim and maybe an eighth of an inch of skin, Gary was rolling on the ground incapacitated. I bravely ran away while Steve dealt with the consequences of his actions. The bruise a week later was impressive.

This is a long ramble on the treatise of “don’t overthink the bisket... and don’t worry about advertising and guys arguing about “who would win, Bruce Lee or Chuck Norris or Darth Vader.” It’s all good.
 
Where are you getting these descriptions?
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Hornady website. https://www.hornady.com/support/duty-defense-differences

Midway and Lucky Gunner published the numbers.

I see now that Critical Defense is a 125gr and Critical Duty is 135gr. So, maybe that influences it.

So, I've noticed I get a bit uncomfortable when recoil hits 550 lbs, using other brands of ammo (mostly Federal, it's available here). It's not so much that it hurts my hand, it's the SOUND! just freaks me out and makes me grind my teeth. All I know is when I fired a 44 mag @ 1,000 ftlbs I decided I'd never do that again. Odly, I never fired a 45 I did not like. For some reason I found them all mild to manageable.


So, I was thinking Critical Duty @ 450 ftlbs would be good, it still expands well. Maybe I'll just have to try both after all. Was hoping to save the cost of a box of ammo.

I should have mentioned, these are for my 4" 686.
 
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The confusion comes from overgeneralizing from Hornady's general remarks.

Hornady's speeds are from a 8" barrel.

Hornady says 'not excessive recoil' for their Defense load. Hornady's 357 magnum speeds are from a 8" barrel, and their speeds are not very high for shooting them from a 8" barrel. They are in fact, watered down 357 magnums. Hornady's 1500 fps with a 125 grain bullet in the Defense line is not very fast. A 'normal' full power 125 grain bullet hits 1450 fps from a 4" barrel. Adding 4" to make it a 8" barrel should add about 200 fps, making it 1650 fps, or more. I get a factory Remington 125 SJHP running over 1700 fps from a Ruger 6.5" barrel. But the Hornady Defense load is made for optical performance in a short barrel.

Hornady's 135 grain Duty round at 1275 fps from a 8" barrel is also slow. A normal full power 158 grain bullet goes 1240 fps from a 4" barrel. I get 1350 fps from factory 158 grain ammo in my Ruger 6.5" barrel.

So, they do qualify as 'not excessive recoil' because neither of them are full power loads which would produce more recoil.

Hornady does not say the Duty round has more power. It says they are 'full power loads' for semi-auto pistols - important to know that they will cycle reliably. But it doesn't apply to their 357 magnum revolver ammo because revolvers don't need to cycle. And their 357 loads are not full power loads. See previous comments.

One selling point Hornady has tried to make is that they don't always need top speed to get their bullets to perform to FBI standards. So, they don't load them as fast as normal full power ammo. If you don't need the extra speed, then load them lighter, and this will reduce recoil.

I hope this helps.
 
Describing recoil is like trying to describe eating chitterlings.

There are so many variables affecting recoil that only by actual shooting the gun/load combinations yourself can any decision be reached. And, make no mistake about it, muzzle blast must be taken into consideration as it affects the general comfort of firing the gun. A .357 Magnum cartridge fired in a heavy Ruger Blackhawk will definitely feel different than when fired in a lightweight S&W. And the "recoil" will be perceived differently when fired in a 2" barrel as opposed to a 4" barrel. And rubber grips versus wood or plastic.

Sitting down and crunching numbers just can't replace actual firing of the gun and ammunition.


Bob Wright
 
& yet one more variable - that seems to get overlooked all the time is - - the actual rate of burn the powder has.

I have shot .44 mag 240 grain LSWC loads using Bullseye that will set your teeth on edge & you will think they are doing 4000 fps. They also leaded the barrel so bad they would cause keyholing & total loss of accuracy after a few shots.

I have also shot .44 mag 240 grain LSWC loads using 2400 that were just on the other side of mild feeling.

Both loads were within a 100/150 fps of each other.

Also - keep in mind that when pressures are considered - thos figures refer to peak pressure, not sustained pressures.

John Schaefer, - aka Fr.Frog - does a good job of going over some of the basis of internal ballistics:
https://www.frfrogspad.com/

Another interesting look at the actual way to measure & graph it is here:

https://www.shootingsoftware.com/pressure.htm

This is rifle oriented, but, it gives you some kind of idea about the pressure curves involved and a measure of dwell time vs pressures & velocity.
 
Another thing....
So, I've noticed I get a bit uncomfortable when recoil hits 550 lbs
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You are actually referring to muzzle energy there, not recoil. I suppose that readers figure out what you mean; it is better, though, and clearer to be exact.
Here is a link to a recoil calculator that will give you exact info.

http://www.shooterscalculator.com/recoil-calculator.php

For instance, a loaded Colt 1911 weighs 48 oz. Five grains of Bullseye powder will push a 230 grain bullet at 850 fps. Using that calculator, i am told that free recoil is 5.17 ft.lbs and the recoil velocity is 10.5 fps.
Now....a Glock 36 (27oz loaded) using the same load has these figures (using 750 fps because of the shorter barrel)...free recoil is 6.87ft.lbs and....watch this....recoil velocity is 15.67 fps.
Same load at less velocity in a lighter gun smacks harder.
Note that recoil velocity is often not discussed but is a big factor in how we perceive.
If you were to consider this pairing on the basis of muzzle energy, the 1911 has a ME of 369 ft.lbs and the Glock is at 295. Yet the Glock has the greater free recoil and is much less pleasant to shoot (my perception)
Last and most important Is the recoil impulse. For the 1911 it is 0.98 lb/secs. For the Glock it is 0.88 lb/secs. Again....the Glock has the greater/heavier/stronger/faster result.
 
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Recoil is no where near as simple as described by the posts above. For instance, the recoil is not just the result of the weight and velocity of the bullet being accelerated. It's calculated by the sum of all of the masses being accelerated so the powder and gasses produced also are included. Then there is the velocity of the acceleration as mentioned by some. The combination of recoil energy and recoil velocity constitute what we call recoil.

However, then there are the mechanical parts of recoil that affect how it's perceived by the shooter. Weight of the firearm being only one. In a pistol, the height of the bore axis above the grip hand also plays a major roll in felt recoil as the higher the bore axis, the more torque force is applied and the higher the recoil forces. That's why revolvers tend to feel like they recoil more than semi-autos because their bore axis is so much higher.

In addition, the shape of the grip and how the shooter grips the pistol has a large affect on recoil and how it's transmitted to the shooter. Again, revolvers have grips that are largely inverted cone shaped making them harder to grip tightly than semi-autos.

Then there are the shooters themselves. A light weight person is going to absorb the recoil energy as a higher percentage of his/her total mass than one who is much larger. Also, a small person with short arms and small hands will feel the recoil differently than one who's large with large arms and large hands.

And on and on.
 
All I know is when I fired a 44 mag @ 1,000 ftlbs I decided I'd never do that again. Odly, I never fired a 45 I did not like.
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I'm making an assumption that the .45 is a semi-auto, and the .44 mag is a revolver. Don't forget that the slide absorbs recoil on a semi to operate, and the same round fired out of a revolver will send more energy into your hands.

This, imho, is the thread winner:
When I was a kid my friend Steve shot his older brother Gary in the butt with a .22 CB cap as Gary was a mean big brother. Even though it only penetrated two layers of denim and maybe an eighth of an inch of skin, Gary was rolling on the ground incapacitated. I bravely ran away while Steve dealt with the consequences of his actions. The bruise a week later was impressive.
Click to expand...
 
Recoil is no where near as simple as described by the posts above. For instance, the recoil is not just the result of the weight and velocity of the bullet being accelerated. It's calculated by the sum of all of the masses being accelerated so the powder and gasses produced also are included. Then there is the velocity of the acceleration as mentioned by some. The combination of recoil energy and recoil velocity constitute what we call recoi
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Actually it is that simple.....if you wish to determine free recoil. What does get left out frequently is the Velocity of the powder gases. Powder charge gas velocity (VC)is a constant in the formula (when it is used). The figure that has been adopted is 4000 fps. Since it is the same for all cartridges, is often left out ( though actual velocities vary from 3700 fps to 4300 fps for centerfire guns).
It is Perceived Recoil that has all those pesky variables. You are surely correct about that.
One important variable that has been left out is Experience. The more familiar a shooter is with shooting in general and a specific weapon in particular, the greater the chance that they will have a different take on Perceived recoil than a new shooter.
 
darkgael said:
What does get left out frequently is the Velocity of the powder gases. Powder charge gas velocity (VC)is a constant in the formula (when it is used). The figure that has been adopted is 4000 fps. Since it is the same for all cartridges, is often left out ( though actual velocities vary from 3700 fps to 4300 fps for centerfire guns).
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4000 fps is not universally accepted.

SAAMI uses different values for different guns that are a multiple of the bullet's exit speed.

High powered rifles = 1.75
Shotguns (average length) = 1.50
Shotguns (long barrel) = 1.25
Pistol & revolvers = 1.50

https://saami.org/wp-content/uploads/2018/07/Gun-Recoil-Formulae-2018-07-9-1.pdf
 
Perceived recoil is different for each shooter and just in the grips alone can make a difference. With the original wood grips my S&W Model 29 sort of stings but using the Pachemyer rubber grips is very manageable. The next person may not feel the way I feel and there is no formula for felt or perceived recoil.

If anyone has read Julian S. Hatcher's notes Hatcher puts quite a bit into Recoil Energy starting around page 283. Additionally SAMMI has a paper on the subject which is also a good read. A free PDF of Hatcher's Notebook can be had online with a little Google effort.

There are also some pretty good final year engineering thesis written on the subject of FRE (Free Recoil Energy) I saw online several years ago. Some went as far as using sensors to measure the recoil energy which were interesting. Well interesting in that their research included help from Sierra and Weatherby. :)

Something I noticed which was amusing was there are a number of FRE calculators online and if you put the same date into a dozen you get 6 different answers for the same data. Go figure huh?

Ron
 
You can basically ignore the contribution of powder, for the sake of the calculation -- it's a tiny correction. When you do that, things get really simple.

Momentum conservation (momentum = p = mv) will imply p(gun) = p(bullet)

Kinetic energy (E) is 1/2 m v^2, or in other words E = p^2 / 2m

So, E(gun) = p(gun)^2 / 2 m(gun) = p(bullet)^2 / 2 m(gun) = m(bullet)/m(gun) * E(bullet)

That's the final result: E(gun) = m(bullet)/m(gun) * E(bullet)

The ratio of the bullet mass to gun mass tells you what fraction of the bullet energy the gun is delivering to you in recoil energy. Notice that if the gun was the same mass as the bullet, the gun would have the same energy in recoil as the bullet has energy. But if the gun has hundreds of times more mass that the bullet, the bullet ends up with 99%+ of the kinetic energy. That's why a recoiling rifle (with momentum equal to that of the bullet) is no big deal for your shoulder, but the bullet can blow the living crap out of the target.
 
I'm making an assumption that the .45 is a semi-auto, and the .44 mag is a revolver. Don't forget that the slide absorbs recoil on a semi to operate, and the same round fired out of a revolver will send more energy into your hands.....
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Don’t forget that there are no .45 ACP loads producing anywhere near 1000 ft-lbs. That has far far more influence on felt recoil than a spring and a slide.....

And while some may believe that powder weight makes no difference in felt recoil, IME lighter charges of faster powder can produce noticeably lower felt recoil than heavier charges of slower powder. Compare .44 magnum recoil between equal velocity loads using H110 and BlueDot and tell me what you think. Like “killing power”, it is difficult to quantify “felt recoil” because individual animals (including humans) react differently to applied forces.

.
 
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