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Old January 11, 2019, 11:36 AM   #1
USNRet93
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Bullet weight and recoil?

So, 2 people have told me different answers to same question..with same 'powder' load, which bullet weight has more recoil? A lighter one or a heavier one? 115gr or 124 gr? 9mm?
Not a physics guy..
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Old January 11, 2019, 11:48 AM   #2
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For every action there is an equal and opposite reaction. What ever muzzle energy is going out the front is going to generate the same going back.
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Old January 11, 2019, 12:16 PM   #3
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Also don’t forget that for the same recoil energy in 2 different rifles, the sharper recoil will more likely come from a rifle that is bolt or lever action vs. semi or a rifle that doesn’t distribute the energy over 200 milliseconds vs 2 milliseconds.
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Old January 11, 2019, 01:12 PM   #4
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Muzzle energy (kinetic) equals one-half the mass of the bullet times velocity squared. E=.5mvv
Load them up and shoot them over a chronograph. Measure the velocity of several shots to get an average. A little math and you'll have your answer. The greater muzzle energy will have the greater recoil.
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Old January 11, 2019, 01:28 PM   #5
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Everything else being equal, the heavier bullet will have more recoil than the lighter bullet.
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Old January 11, 2019, 01:38 PM   #6
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IMO that is a more complicated question beyond the pure physics than it may first seem as recoil experiences are somewhat subjective in a semi automatic pistol due to the characteristics of the recoil. I find I like shooting 147 gr vs 124 in 9MM as it seems to be more of a push and less of a snap that 124.
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Old January 11, 2019, 01:43 PM   #7
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I don't think this question has a simple answer.

The "power factor" that is used to determine classes in USPSA and IDPA competition is a measure of projectile momentum. It is based on a simple product of projectile mass and muzzle velocity (momentum=mv), specifically projectile mass in grains x muzzle velocity in feet per second divided by 1000.

Conservation of momentum is an important law of physics governing the interaction and movement of bodies. This law would suggest that the momentum imparted to the projectile by the expansion of gasses in the barrel will equal the momentum imparted to the slide.

But perceived recoil may depend on more than just slide momentum even when shooting various cartridges from the same handgun. The velocity imparted to the slide might significantly affect the perceived recoil. Projectiles that leave the barrel more slowly might therefore result in somewhat slower slide velocity.

Here is a somewhat interesting article which attempted to control for barrel length and pistol weight, measuring magnitude of recoil based on the extent of pistol movement when it was fired clamped into a Ransom rest:

http://www.handgunsmag.com/editorial...ridges/137951#

The authors also attempted to control for different powders and powder charges used in different commercial loads by firing hand loaded cartridges that had been charged with the same powder.

They then adjusted the hand loads to match the same power factor comparing .45 ACP to .40 S&W and 9 mm Luger to 38 Super.

They found that when the power factor was matched the recoil, as measured by Ransom rest pistol movement was virtually identical for .45 ACP compared to .40 S&W, and for 9mm Luger compared to 38 Super. This makes sense to me since they controlled for pistol weight. Therefore the momentum imparted by the powder charge to the projectile (power factor) would equal the momentum imparted to the pistol which would result in equal movement of the pistol within the rest, given the same pistol weight.

The measured recoil of .45 ACP and .40 S&W was quite similar even when powder charge and power factor were not adjusted for. But as many who shoot both calibers would say, .45 ACP recoil is often perceived as a slower "push" whereas .40 S&W recoil is perceived as a sharper "snap". The authors opined that the faster .40 S&W projectile which dwells in the barrel a shorter time than the .45 ACP projectile, produces a faster recoil impulse. This makes sense to me.

If you have an accurate measure of muzzle velocity, projectile momentum is easy to calculate for any given projectile mass. It is momentum in lb-ft/sec equals projectile mass in grains times muzzle velocity in feet per second divided by 7000. If you compute the projectile momentum for similar 9 mm Luger loads (FMJ from the same maker, for example) for 115, 124, and 147 grain projectiles, you will usually find that the momentum increases by 0.8-1.0 lb-ft/sec as you step up each projectile weight. That would imply that the recoil will increase with increasing projectile mass. But those heavier projectiles also have lower velocity and dwell in the barrel longer, so the velocity imparted to the slide might be less.

For what it is worth I have heard some claim that 115 grain produces more recoil than 124 grain when shot from the same gun, and some the opposite. And I have heard some say the 147 grain shoots softer than 124 grain, and some the opposite.
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Old January 11, 2019, 01:47 PM   #8
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Of course it has a simple answer.
Heavier.
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Old January 11, 2019, 01:58 PM   #9
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A heavier bullet requires more energy to move it.. Because it is harder to move, chamber pressures in all directions also increase. So yes, the heavier the bullet the greater the felt recoil. Simple answer..
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Old January 11, 2019, 02:14 PM   #10
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Doesn't matter what your opinion is about it, the law of physics are set in stone. Newton got it right hundreds of years ago. The simple answer is heavier.
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Old January 11, 2019, 04:20 PM   #11
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Thanks
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Old January 11, 2019, 04:47 PM   #12
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I find 165 grain .40 S&W less pleasant to shoot than 180 grain, as do many others. So the heavier results in more perceived recoil does not necessarily always apply.
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Old January 11, 2019, 05:35 PM   #13
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If the light and heavy bullets are both moving at the same velocity, then the heavier bullet would have more muzzle energy, and according to Newton more recoil...all else being equal. Typically, the lighter bullet is moving faster than the heavier bullet because we adjust the powder charge. Since velocity is squared in the equation, that would have much more impact on recoil.
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Old January 11, 2019, 05:44 PM   #14
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Recoil is made up of 4 things that all are important.

Weight of the projectile
Weight of the powder charge
Weight of the firearm
Velocity of the projectile


If the weight of the projectile goes up and the powder charge and velocity remain the same you get more recoil


BUT.... When you go up in bullet weight in the same cartridge the powder charge will be less and velocity will be less.

It is a complicated issue with no easy answer.

You also have to consider recoil velocity. If 2 guns have exactly the same recoil in ft lbs, it is very common for one of them to recoil FASTER. That will make recoil SEEM like it is hitting you harder than another gun that spreads the same exact recoil out over a longer period of time. Generally heavier bullets recoil slower than lighter, faster bullets.

Quote:
Of course it has a simple answer.
Heavier.
A 35 Whelen with a 250 gr bullet has almost exactly the same recoil as a 300 WM shooting 180 gr bullets. The 300 uses about 50% more powder and is shooting a lighter bullet about 600 fps faster.

But because of recoil velocity most people find a 35 Whelen more comfortable to shoot.

Plug in the numbers here and stop guessing

http://www.handloads.com/calc/recoil.asp
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Old January 11, 2019, 05:49 PM   #15
Jim Watson
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If the OP really means the OQ
"with same 'powder' load, which bullet weight has more recoil? A lighter one or a heavier one? 115gr or 124 gr? 9mm?"

Then the heavier bullet will have the greatest recoil.
For many powders, a maximum load for a 147 is a starting load for a 124 and a powderpuff load for 115 grain bullet. Velocity is not much different so the heavier bullet will have the most momentum.
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Old January 12, 2019, 12:31 AM   #16
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Here's an answer based on data. The question was which produces more recoil when they use the same powder load. The answer depends on what actually happens when bullets of different weights get the same load.

The answer is: generally, the heavier bullet will produce more recoil. Now let's qualify that with data. With handgun rounds, generally, the heavier bullet can actually go faster than the light bullet when they are loaded the same.

The data at this link shows what happens when you load different bullet weights with the same powder charge. See Table 2. http://www.shootingtimes.com/editori...ves-edge/99399 It is 45 Auto data but there's no reason to think it's different in the 9mm.

Since the heavier bullet is going faster, or at least around the same speed as lighter bullets, it will produce more recoil.

There are some caveats for this data. The bullets need to be the same shape and seated to the same OAL. If you start changing bullet shape or OAL, the answer might change because both of these can have a significant effect on velocity (and pressure) and these can alter the recoil.

The article at that link explains the effect of bullet weight on recoil when the different weights are loaded to the same power factor, something that other folks have mentioned. I won't bother with that since that was not part of the original question.
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Old January 12, 2019, 01:04 AM   #17
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Recoil is proportional to muzzle momentum, not muzzle energy.

Multiply the bullet weight by the muzzle velocity for that bullet and compare it to the same product for the second loading.

The loading with the larger weight-velocity product will recoil more.
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Old January 12, 2019, 01:28 AM   #18
74A95
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Quote:
Originally Posted by pblanc View Post
Here is a somewhat interesting article which attempted to control for barrel length and pistol weight, measuring magnitude of recoil based on the extent of pistol movement when it was fired clamped into a Ransom rest:

http://www.handgunsmag.com/editorial...ridges/137951#

The authors also attempted to control for different powders and powder charges used in different commercial loads by firing hand loaded cartridges that had been charged with the same powder.
Not sure why you say 'authors' and 'they'. There is only one author.

Last edited by 74A95; January 12, 2019 at 04:37 AM.
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Old January 12, 2019, 04:05 AM   #19
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Quote:
Originally Posted by LineStretcher
A heavier bullet requires more energy to move it.. Because it is harder to move, chamber pressures in all directions also increase. So yes, the heavier the bullet the greater the felt recoil. Simple answer..
Not so simple. Remember, the question stipulates two bullet weights with the same powder charge.

Quote:
Originally Posted by USNRet93
with same 'powder' load, which bullet weight has more recoil? A lighter one or a heavier one? 115gr or 124 gr? 9mm?
The fundamental rule of Physics is "For every action there is an equal and opposite reaction." The action in firing a handgun is the rapid combustion of the powder. This combustion generates energy/force. This energy/force acts equally in all directions. Radially, the force is constrained by the surrounding cartridge case and barrel. That leaves two directions in which the energy can act -- forward (pushing the bullet), and rearward (pushing the slide and then the firearm).

In this case, since the powder charge has been stipulated to be the same, what's going to change is how fast the charge can push the bullet. It's axiomatic that for the same powder charge a heavier bullet will result in more felt recoil than a lighter bullet. This appears, at first, to be contradictory. Since the force is acting on a lighter bullet, it would seem that the opposing force (recoil) would also be less. The overlooked factor is that the lighter bullet accelerates faster and exits the barrel sooner. As soon as the bullet leaves the barrel, there's nothing there for the column of expanding gas to push against. From that point forward in time, any gas left in the barrel and chamber basically dissipates without adding anything to bullet velocity or recoil.
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Old January 12, 2019, 04:36 AM   #20
74A95
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Quote:
Originally Posted by Aguila Blanca View Post
The overlooked factor is that the lighter bullet accelerates faster and exits the barrel sooner.
The light bullet generally goes slower than the heavier bullet (see the link in my previous post), so I'm not sure it will exit the barrel sooner.

Quote:
As soon as the bullet leaves the barrel, there's nothing there for the column of expanding gas to push against. From that point forward in time, any gas left in the barrel and chamber basically dissipates without adding anything to bullet velocity or recoil.
The exiting gas does add to the recoil, in accordance with "for every action there is an opposite and equal reaction" - just like you said. The gas exits at speed, faster than the bullet exits, producing a forward force. This creates a reciprocal backward force. https://en.wikipedia.org/wiki/Recoil...he_ejected_gas

Formulas that calculate recoil require the weight of the powder to be included in the calculation of the recoil force in accordance with the conservation of mass. The powder weight is considered part of the ejecta. e.g. http://kwk.us/recoil.html

And there's this: http://www.shootingtimes.com/editori...-recoil/328788
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Old January 12, 2019, 02:15 PM   #21
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Quote:
Originally Posted by JohnKSa View Post
Recoil is proportional to muzzle momentum, not muzzle energy.

Multiply the bullet weight by the muzzle velocity for that bullet and compare it to the same product for the second loading.

The loading with the larger weight-velocity product will recoil more.
Yes, that was the point I was trying to make in a much more long-winded way. Yes, there is a law of physics that deals with conservation of energy, namely the first law of thermodynamics, but if we are talking about physical laws describing the relative motions of objects that collide, or in this case two objects that are affected by an "explosion" between them, it is the law of conservation of momentum that applies.

I know the OP asked about cartridges with different mass projectiles and the same "powder" load, but I am not sure if the intent of the query was to ask what happened with exactly the same type of powder and charge weight in the same cartridge case.

I had assumed that the intent of the question was to determine what the difference was in recoil was with very similar types of ammunition, say standard pressure (P) FMJ loads in the same caliber made by the same manufacturer. Because commercial ammunition with different projectiles is not loaded with the same exact powder charge and type, nor is it loaded to achieve the same power factor across all different projectile masses. Commercial ammunition is loaded to achieve a desired maximum case pressure per SAAMI standards.

If you look at 115, 124, and 147 grain 9mm loads from a variety of different manufacturers, you will invariably see that the advertised muzzle velocity increases as projectile mass decreases. This is true for calibers other than 9 mm Luger as well. But while projectile momentum often increases with increasing projectile mass, it does not do so invariably.

For example, if you look at American Eagle 9mm FMJ ammunition, the advertised muzzle velocities for 115 grain, 124 grain, and 147 grain respectively are 1180 fps, 1150 fps, and 1000 fps respectively. The computed projectile momenta are 19.4 ft-b, 20.4 ft-lb, and 21.0 ft-lb, so in this case momentum does increase slightly with increasing projectile mass.

But if you look at CCI Speer Lawman FMJ, the muzzle velocities for 115 grain, 124 grain, and 147 grain are 1200 fps, 1090 fps, and 985 fps and the calculated momenta are 19.7 ft-lb, 19.3 ft-lb, and 20.7 ft-lb. In this case, the momentum for the 115 grain load is greater than that of the 124 grain.

And to look at another caliber, for American Eagle .40 S&W FMJ, the muzzle velocities for 155 grain, 165 grain, and 180 grain are 1160 fps, 1130 fps, and 1000 fps. In this case the momenta are 25.7 ft-lb, 26.6 ft-lb, and 25.7 ft-lb. The intermediate projectile mass has the greatest momentum.

As has been demonstrated, recoil measured by movement of the pistol in a Ransom rest is determined by projectile momentum, or power factor, which is basically the same thing. But I do suspect that projectile dwell time within the barrel has an effect on the acceleration of the slide in recoil, which has an effect on perceived recoil.
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Old January 12, 2019, 06:06 PM   #22
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Quote:
Originally Posted by pblanc
I know the OP asked about cartridges with different mass projectiles and the same "powder" load, but I am not sure if the intent of the query was to ask what happened with exactly the same type of powder and charge weight in the same cartridge case.

I had assumed that the intent of the question was to determine what the difference was in recoil was with very similar types of ammunition, say standard pressure (P) FMJ loads in the same caliber made by the same manufacturer. Because commercial ammunition with different projectiles is not loaded with the same exact powder charge and type, nor is it loaded to achieve the same power factor across all different projectile masses. Commercial ammunition is loaded to achieve a desired maximum case pressure per SAAMI standards.
Unless the OP revises the question, why don't we proceed on the basis that what he asked was what he wanted to know, rather than changing the question to what we want to talk about?

I load mostly for .45 ACP. I have a load that uses 5.3 grains of Winchester 231 behind a 230-grain plated lead round-nose bullet. I also have a load that uses the same 5.3 grains of Winchester 231 behind a 185-grain plated lead round-nose bullet. Same cartridge, the exact same powder charge -- which is what the original question asked.

The 185-grain cartridges produce significantly less felt recoil.
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Old January 12, 2019, 08:09 PM   #23
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74A95 --- Thanks for the link to the article from Shooting Times. It explains very clearly and authoritatively what is happening.
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Old January 12, 2019, 09:02 PM   #24
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Quote:
Originally Posted by KyJim View Post
74A95 --- Thanks for the link to the article from Shooting Times. It explains very clearly and authoritatively what is happening.
You're welcome.
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