I have always understood that a heavier bullet will recoil more in a gun than a lighter bullet does as recoil is a result of both weight and velocity but with weight having a greater influence.

That was my understanding behind the 125/135 gn .357 Magnum being more controllable than a 158 gn bullet.

But yesterday I had someone with a lot of experience tell me (insist) that a lighter bullet recoils more because of the velocity. This person insisted that a 147 gn bullet in 9mm recoils less than a 124 gn bullet because it is going slower.

Which is right?

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View from down under

Conservation of momentum (recoil) vs. conservation of energy (ability of bullet to do work on the target) favors lighter bullets moving at higher velocity.

Kinetic energy is 1/2 (mass) X (velocity) squared. So, increases in velocity have more effect on energy than mass. A heavier, slower bullet 'may' generate less energy than a lighter, faster bullet depending on how much slower, using the above equation.

However, recoil (how much perceived "kick" by the shooter) is also dependent on the gun used. A flyweight subcompact 9 mm will recoil much more than a steel 1911.

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Alan
SWCA LM 2023, SWHF 220

This is my understanding of how it works...

Take two loads with the same muzzle energy, a slow-heavy load and a light-fast load, fired by the same shooter from the same gun. They have the same energy, so the recoil energy would also be the same ("equal, but opposite...etc.").

The difference is in how that energy is perceived by the shooter. The slow-heavy bullet, being slow, takes longer to accelerate, so the recoil force the shooter feels will be more like a push, because that energy is delivered over a longer period of time (even if it's measured in fractions of a second). The light-fast bullet accelerates faster, so it will deliver it's recoil energy more quickly, and will feel like a snap.

I will freely admit I could be wrong, but it does seem to make sense to me based on experience.

With 9mm, not enough recoil difference to concern yourself with. Use something that shoots well for you; bullet weight is very secondary.

For a 9 mm in 115 gr going supersonic, there is more recoil felt, than from a heavier bullet going subsonic. But if we matched the energy and velocity, the heavier bullet would have more recoil.

158 grain and 180 grain 357 magnum have more recoil than 125 grain.

For a 500 magnum, there is more recoil in a heavier bullet weight of 500-700 grains versus 325 or 350 grain bullets.


Sent from my iPad using Tapatalk Pro

^^^This is my understanding of how it works as well^^^
Physics is physics, and equal ME means equal forces, means equal amounts of work being done.
Work = mass moved over time.

A milder longer PUSH vs a sharper shorter SLAP
As a rule the heavier bullet will FEEL like it gives less recoil (a.k.a. less perceived recoil).

I'm all in with ContinentalOp & BC38, I always use the terms "push" vs "snap". I first realized it with the 45 Colt revolver and the 45 acp. auto. Always thought the 45 auto felt a bit snappier than the Colt revolver.

A larger weight bullet does not have to have more recoil if it is
slowed down.

I can load my 30-06 with a 180gr to shoot with the recoil of a 30/40 Krag or my .270 to have the recoil of a 257 Roberts.

Lots of my 9mm 124gr are the speed of a 4" 38 special.

However I am still young enough to enjoy full loads every now and then at the range, but that is with 6" heavy frame weapon
with the .357 in at least a L frame, to reduce the recoil.

The weight of the weapon plays a large part in how much recoil
you will receive with full loads.

Are you thinking of shooting .357 mags in an "Airweight" , to
see about control ??

I want pictures !!

Continentalop stated the OP's answer correctly but I would like to clarify just a little......."Perceived Recoil" is what we are discussing, not muzzle velocity or muzzle energy. The factor of great importance to Perceived Recoil is the time taken by the bullet from ignition to exit of the barrel. A light bullet takes milliseconds less time than the heavier bullet. A heavier bullet is imparting heavier felt recoil all the time until leaving the barrel. With the same sight setting a heavy bullet will cause the muzzle to raise higher during recoil than the lighter bullet and usually causes the heavier bullet to strike the target higher than the lighter bullet. The sensation of recoil perceived by the shooter is longer for the heavier bullet. That translates to our hand, nerves and brain as "heavier" recoil. Usually, the heavier recoil causes the muzzle and the entire handgun to raise higher for the initial shooting position and will give longer times for recovery and re-aiming on subsequent shots. Once I figured that out I favored the lighter bullets in most calibers because of the desire to improve shot time between shots after the first shot. Of course the necessity to make all shots "hits" intensifies.

If you look just at the bullet and gun conservation of momentum means the percentage of energy you feel as recoil is proportional to the total energy divided by the combined weight of the gun and bullet. For example if you have a 2 pound (14000 grain) revolver firing a 125 grain bullet generation 550 ft-lbs of energy the recoil energy would be 550 *125 / (14000 + 125) = 4.9 ft-lbs. The bullet would have 550 * 14000 / (14000 + 125) = 545. ft-lbs of energy. With a 158 grain bullet and the same energy level the recoil energy goes up to 6.1 ft-lbs.

But that math leaves out a lot of variables.

1 - Typically heavy bullet loads generate less energy. Speers 125 grain 357 gold dot is rate at 580 ft-lbs and their 158 grain Gold Dot is rated at 530. When you look at the difference in calibers like 9mm and 40 S&W where heavy bullets don't leave enough room for powder the difference is more pronounced.

2 - It doesn't include the effect of the powder. After the bullet exits the barrel the still burning powder acts like a rocket aimed into your hand. The more powder that remains after the bullet exits the greater this effect will be. The more pressure that remains the greater this effect will be. It is one of the reasons short barrelled guns have more recoil. It seems like heavy bullet loads burn more of the available powder and this factor favors heavy bullets.

3 - Perceived recoil can be affected by how loud a gun is. Maybe this one is just me but even with good hearing protection loud guns seem to have more recoil. This is entirely psychological so it is going to vary a lot from person to person. Light bullet loads tend to be louder.

4 - How tightly you hold the gun. When you firmly grip a handgun or pull a rifle tightly into your shoulder you add some of your body mass to the mass of the gun. Tightly held firearms don't just feel like they have less recoil, they actually HAVE less recoil.

5 - It doesn't take into account how the recoil impulse is spread out. A semiauto that spreads out the recoil energy is going to be less punishing than a revolver firing the same cartridge.

The engineer in me really wants there to be a simple mathematical formula for predicting recoil. But all the added variables I listed here and others I haven't thought of make that impossible. So I end up going with what I have learned from 30 years of shooting. With handguns ammo with light bullets being pushed as fast as possible will make me more likely to flinch than ammo with heavy bullets being pushed as fast as possible. With rifles the reverse is true. How likely I am to start flinching (or anticipating the shot as it is now called) is not the same as true recoil it is what matters most to me.

As for a 33oz. 9mm pistol's Recoil, per loads.......

115gr
1033fps R 2.88
1350 ........ 5.16 pf155

124gr
1024fps .... 3.28
1267 ......... 5.17 pf157

135gr
907fps ....... 2.95

147gr
890 ........... 3.32
1040 ......... 4.76 pf153

please note the difference in PF and recoil with the loads.

Later.

The grips on the gun and how they affect your grip on the gun also can change the felt recoil considerably. Different grips can change the amount of area receiving the blow and if the force is coming straight back or going in to muzzle rise.

At equal flt lbs recoil will be about the same,
At equal power factor.. ( straight mass X velocity) heavier bullet will recoil less, assuming same powder charge.
In the same gun, perceived recoil is a factor of bullet weight, powder weight, and powder burn rate. I honestly dont think velocity matters,, as its basically a function of powder weight and burn rate.
Slower powders produce more muzzle jet action and use heavier charges to reach the same velocities, yet produce more recoil..
Just shoot a 9mm 125 light charge of fast powder in a compact 9mm against a 125 gr 357 magnum in a snubby.
Same work, same bullet mass, grossly different recoils.
So really you cant say, "Heavier bullets recoil less or more" both statements would be wrong without taking into consideration other factors.

I think we're getting way off into the weeds here.

Obviously if you change from a revolver to a semi-auto it is going to make a difference. So will changing grips, or firearm weight, or barrel length, or powder burn rate, or any number of other factors.

The question (and the point) is with all else being EQUAL, will a heavier bullet propelled by a smaller charge or a lighter bullet propelled by a larger charge give more recoil?

If the PF and ME are the same the amount of recoil energy will be the same. The PERCEIVED recoil may very well be different since the light bullet with its larger charge of powder, and it's corresponding higher velocity, will cause the recoil pulse to be shorter, sharper, and therefore FEEL more violent.

Kind of like comparing someone giving you a hard PUSH against your cheek vs. them SLAPPING you on the cheek. Both may have the same energy and move your head the same distance, but the slap will hurt more and that will make it seem more violent. That's how I see the difference in perceived recoil.

Since no one (except maybe Ed ) measures recoil with instruments, most of us only have the recoil we feel (perceive) when we shoot to evaluate. So that is what we are talking about here.

All I now is my 12 ga kicks a lot harder with a punkin' ball than with a light skeet load. You can run whatever formulas you want, but that punkin' ball still kicks harder.

There is a formula for free recoil, I just spent 10 minutes looking for it without success. I'm going to keep looking. Found a formula. This is really intended for long guns and doesn't take reciprocating parts into account.


Free Recoil= M x V squared

V=(projectile weight gr+ [powder weight gr x1.75]) x muzzle velocity f/s divided by gun weight in grains.

Gun weight lbs x 7000= gun weight in grains.

M= gun weight in pounds/64.32

Going through this with a 2.5 lb gun firing a 115 gr bullet, 6.2 gr powder at 1150 f/s we have 2.7 ft lbs of recoil.

A 147 gr bullet, 4.3 gr powder at 920 f/s in the same gun gives 2.56 ft lbs of recoil.

A +P 124 gr loading using 6.4 gr of powder producing 1180 f/s, same gun gives 3.22 ft/lbs.

Going back to Kiwi Cops original question, running the current Hornaday specs for 125 gr & 158 gr .357 loads using 296 powder shows no significant difference in free recoil. Perceived recoil may be an entirely different matter, the formula above doesn't take powder burning rate into account. FWIW, momentum/power factors for the two loads do show a difference : 187.5/125 and 197.5/158, about 5%.

IIRC, the original ammunition requirement for IPSC .357 used the 125 gr load. It had the lower power factor. It was also obviously more effective.

Interesting article in August issue of Shooting Times. Talks about the weight of the powder and its effect on recoil. Talks about 4 values used to calculate recoil force. Bullet weight,bullet speed, weight of firearm and weight of powder.
While it is interesting it is above my pay grade of fully understanding. It mentions the powder(gas) coming out of the barrel,its weight or value assigned to it. Even SAAMI accepts this.

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U.S.A.F---E-7--Retired

After all, this is America; if you can't transform something that's very simple into something that's needlessly complicated, it's not worth doing.

I know that the 180 grain Remington 44 mag rounds from Wally World sure seem like they recoil pretty hard. Compared to 240 grain anyway. Lots more fire and ear shattering boom too.

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Bobby SWCA #4067
SWHF #1144

So you're trying to draw some kind of conclusion by comparing a single solid slug of lead that fully plugs the bore to a handful of bird shot pellets that are smaller than grains of rice?

The differences in the physics involved are so huge it isn't even worth discussing. Suffice it to say its like comparing apples to watermelons.

Hay, just a cotton pluck'n, pea pick'n, minute, here........
I resent that remark.

We done have, Watermelon shoot'n in this here, good old, US of A !!

There are several recoil calculators online; plug in the numbers and see which is which

OK OK OK --

Now consider this:

fire a gun with a bullet of infinite weight (or mass) with a charge of any size, and there will be no recoil because a bullet of infinite weight cannot be moved.

Now fire the same gun with a bullet of zero weight (or mass) with a charge of any size, and there will be no recoil because the bullet that isn't there cannot move.

Go figure.

Your first supposition is incorrect. Against an immovable object the recoil would be the full force generated by the exploding powder charge. Recoil isn't the moving of the bullet - recoil is the equal and opposite reaction force from the push that accelerates the bullet. If the bullet doesn't move then ALL of the force generated by the explosion becomes recoil.

Your second supposition is also incorrect. Even without the bullet the forceful ejection of the mass of the burning powder is still going to provide SOME reaction force pushing the gun backwards - kind of like a mini jet engine. It will be minimal, but it won't be zero.

This thread reminds me of a young lady I dated many years ago. She drank rum and diet coke because it had fewer calories than rum and coke.

Yes, empirically, but does that translate into any real-world difference?

She moved away when she got a supervisory job at Treasury, which explains much in my book.

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Certified Curmudgeon

As long as the gun has infinite weight, too.
Just say the chamber is plugged so the bullet can't move. Same as burning something within a sealed vessel strong enough to contain the pressure, no net motion and no recoil.

Wow! I finally gave up hoping to find the answer..... Now, have any of you arrived at the answer? Talk about what does what!
Stay safe
Poli Viejo

In my Kahr KT40, the 165 gr. has less perceived recoil to me than the 180 gr.

Nope. There can be no acceleration without movement. We're talking about the bullet mass. Zero bullet mass then zero bullet movement. Infinite bullet mass then zero bullet movement.

This is a theoretical logic exercise BC38 - not a practical one.

OK - Here is your answer.

If everything else is exactly the same except bullet weight - that includes size, shape, density, composition, volume, powder, charge, etc. then the quantity of recoil energy will be the same. The quality of the recoil profile may be different - longer, shorter, smoother, sharper, etc.

But since everything cannot be the same (a bullet made of the same stuff and being the same size having greater or less mass density is impossible).

You can't get something for nothing.

Theory can't suspend the laws of physics. Ever heard the one about for every action there is an equal and opposite reaction?

Unless you are attempting to redefine recoil to be bullet movement - as opposed to the accepted definition of rearward movement of the firearm in reaction to the acceleration forces ON the bullet (not actual movement of the bullet) - then neither of your examples work.

Neither the bullet moving OR failing to move can zero out the reactive force. Theories that don't take physical realities into consideration aren't valid theories because they aren't logical. They are more akin to believing in magic rather than logic.

Sorry, but ideas don't trump physics. This discussion is about real world physics, not flights of fantasy.

Now, if you are talking about the equations, and substituting zero or infinity into them, then yes, they fail to work when you do that. This isn't anything unusual or specific to these equations. A lot of math doesn't have any real world application (i.e. doesn't work) when you use zero or infinity as variables. You can't divide by zero for example. Nothing particularly interesting or earth shaking about that.

False. weight of the bullet does have a factor in actual recoil; that is Newton

All this theory is fine but in a practical sense I can’t get my head past the fact that a heavier bullet impacts on target higher than a lighter one does. That to me indicates a higher muzzle rise (not all of the impact height difference as trajectory also comes into play) therefore more recoil.

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View from down under

Not quite. Remember that sights are regulated by humans, meaning that the POA-POI relationship takes recoil into account. I'll use a .38 Special snubnose revolver as an example. Typically, they're zeroed for 158gr loads at 7 yards. That means that when you're sights are on a point at 7 yards, the bullet will strike that point.

Now consider the time it takes between primer detonation and the bullet leaving the muzzle. The gun is already starting to recoil before the bullet leaves the muzzle, but the sights take this into account when they're zeroed.

Now take a 110gr bullet, fired from the same gun, at the same point, at the same distance. Let's also assume that the velocity is high enough that it generates the same muzzle energy as the previous 158gr load. To do so, the bullet has to travel at a higher velocity than the 158gr load. This means that it spends less time moving through the barrel, which in turn means that by the time the light bullet exits the muzzle, the gun has moved less vertical distance through the arc of recoil.

The result? The lighter bullet hits the target lower than the heavier bullet, all else being equal.

Clear as mud?

If it is false, and Newton is correct that for every reaction there is an equal an opposite reaction, then a 1000 grain bullet from a .38 special would have more muzzle energy than a 375 H&H with one tenth the powder charge.

I actually heard about this physics stuff long long ago before I became an Engineering Supervisor at one of the National Engineering Laboratories.

So, in theory, if you had a deep enough case and seated the lighter bullet deeper, you could create the same transit time through the barrel and not need adjustable sights.

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Certified Curmudgeon

Hmm...not sure. The problem is that the lighter bullet would have to leave the muzzle at the same time as the heavier bullet, which would mean a lower velocity. However, this would result in less energy than the heavy bullet, including less recoil energy. The muzzle would still rise less than with the heavy bullet so the light bullet would still hit lower. I think. My head hurts now...