Why heavier 9mm rounds like 147 gr feel softer shooting than 115 gr?

[Tango]

When I was a beginner and shooting only factory ammo, I was told to stay away from lighter bullet weights like 115gr, and use 147gr because heavier rounds would recoil lighter. My experience confirmed this: 147gr rounds felt better and easier to control. Physics, however, tells us that recoil is momentum, and a heavier bullet at the same speed would generate larger recoil. So I compared momentum of a typical factory ammo like Speer lawman, at 115 and 147 grains. Based on factory specs, the momentum of the 147gr is actually larger than the 115gr, but by only about 5%. I do not think anybody can notice this difference in their hand, but even if they do, the heavier bullet should recoil more. This is contrary to what people feel. What I believe happens is that because the 115 grain bullet is actually supersonic, it creates blast that makes it feel more "snappy" vs. 147 grain is subsonic and doesnt create the same shock wave and the perceived snappiness. 

[Cuz]

There were a few times when I thought it would be advantageous to switch from 124 to 147 gr Bullets. Then I figured the 147s would be too heavy for the PCC. Then I thought maybe the 115’s would be best in the PCC, and good enough in the pistols. At the time I was shooting Berry’s copper washed Bullets and if I went with 115s, then I’d be driving them close to Berry’s max recommended velocity for their Bullets. In the end I stuck with the 124/125 gr Bullets as the perfect compromise for just about all situations. 

[Guy Neill]

Power factor is a momentum value.

 

Definitely, if you are shooting the bullets at the same velocity, the heavier will recoil more.  However, you are normally shooting the bullets at the same power factor so that the recoil is the same.

 

The heavier bullet, going slower for a given power factor, will take longer to exit the barrel (though not by much), so the recoil is delivered over a longer period of time.

 

Most will not likely notice the time difference.  The choice comes down to what feels best to the shooter, delivering quicker follow-up shots and accuracy.

 

Other factors include the moment arm and the amount of powder.

 

Since the powder charge plays a part in recoil, and the heavier bullets normally use less to make a power factor, the resultant feel is different since the force on the gun changes.

 

As an example, taking some charge weights from one of the reloading manuals, we have, for 9mm,

 

Bullet          Velocity          Charge          Recoil          Force      PF

115               1130               5.2                 2.52            6.4          130

124               1048              4.9                 2.47            5.9          130

147                 884              4.0                 2.34            5.6          130

 

[Cuz]

Thanks Guy. I tend to notice that not many PCC shooters use the 147s, while a good deal of the Production, Carry Optics, and Limited minor shooters seem to love them. Are they not as well suited to PCC?

 

[Guy Neill]

Most PCC's I've seen have compensators.   Compensators work better with more gas, so the lighter weigh bullets, with more powder, give more gas.

 

I've not shot a lot of PCC, but that's the way I would approach it, leaning to using the 124 grain bullets as the middle ground.

 

 

[Tango]

13 hours ago, Guy Neill said:

Power factor is a momentum value.

 

Definitely, if you are shooting the bullets at the same velocity, the heavier will recoil more.  However, you are normally shooting the bullets at the same power factor so that the recoil is the same.

 

The heavier bullet, going slower for a given power factor, will take longer to exit the barrel (though not by much), so the recoil is delivered over a longer period of time.

 

Most will not likely notice the time difference.  The choice comes down to what feels best to the shooter, delivering quicker follow-up shots and accuracy.

 

Other factors include the moment arm and the amount of powder.

 

Since the powder charge plays a part in recoil, and the heavier bullets normally use less to make a power factor, the resultant feel is different since the force on the gun changes.

 

As an example, taking some charge weights from one of the reloading manuals, we have, for 9mm,

 

Bullet          Velocity          Charge          Recoil          Force      PF

115               1130               5.2                 2.52            6.4          130

124               1048              4.9                 2.47            5.9          130

147                 884              4.0                 2.34            5.6          130

 

so, do you agree with my assessment that the so called "perceived recoil" is actually supersonic blast of the lighter 9mm bullets?

[Eric802]

"Supersonic blast" is, well, something I haven't heard of in 40+ years of shooting.  And I can't imagine how it would have any effect on perceived recoil. Unless you're downrange or using a suppressor, any sonic crack is (to me) audibly indistinguishable from the sound of the primer/powder going off.  

[MemphisMechanic]

20 minutes ago, Tango said:

so, do you agree with my assessment that the so called "perceived recoil" is actually supersonic blast of the lighter 9mm bullets?

I do not.

 

My 147gr loads are noticeably softer recoiling than my 124s. With both at ~130-133 power factor, they are both subsonic.

 

It’s a function of HOW you go about reaching that amount of power. This oversimplifies/exaggerates it, but think about sliding your refrigerator across the kitchen to run into somebody’s shin at 3 mph, versus hitting that shin on the corner of the light little coffee table at a full sprint.

 

The same amount of force might be involved in both events, but I’ll take the guy who doesn’t know how to parallel park his fridge. Coffee tables suck.

 

Edited June 23, 2021 by MemphisMechanic

[George16]

17 hours ago, Tango said:

Physics, however, tells us that recoil is momentum, and a heavier bullet at the same speed would generate larger recoil.

This is true if and only if the speed or velocity are the same. However, as @Guy Neillposted, the velocity of a heavier bullet is slower compared to a lighter bullet is lower to achieve the same PF. 
 

Supersonic speed is about 1126 ft/s at sea level. A 115 Gr bullet traveling at that speed has a PF of 129.49. For a 147 Gr bullet to achieve the same PF, it only needs to travel at 880.88 ft/s. With that said, it only requires a considerably smaller amount of powder to achieve that compared to a 115 Gr bullet. So the resulting recoil is less making it “softer shooting”.

Edited June 23, 2021 by George16
Replaced velocity with PF. Thanks @braxton1

[Braxton1]

8 hours ago, Cuz said:

I tend to notice that not many PCC shooters use the 147s, while a good deal of the Production, Carry Optics, and Limited minor shooters seem to love them. Are they not as well suited to PCC?

 

 

When I was running the Chrono at the South Carolina match back in May, I saw a LOT of PCC guys who were using 147/150 grain bullets.  It really surprised me.  Most said that they're doing it because it seems to be softer through their gun. 

 

To me, heavier/slower bullets feel sluggish in both pistol and PCC platforms.  This is totally subjective, but I just feel like the recoil impulse (although more intense) is over faster and the sights begin settling down quicker.  The heavy bullets feel "lopey" (that's a term a friend uses that just sounds right).

 

[Guy Neill]

Recoil is looked at as the kinetic energy of the gun, with the gun velocity found with a momentum balance, as shown in the numbers given earlier that include the gas momentum.

 

The gas jet does do something, but to what degree is unknown.  If it did nothing compensators would not work.  Finding the thrust cannot be accomplished easily,  and since we are already using the gas momentum in the momentum balance, it may be unnecessary. 

 

Thrust requires the mass flow rate and the gas velocity at the muzzle, at least.  A muzzle gas velocity can be approximated only if we know the actual chamber pressure, and varies shot to shot just as the chamber pressure does.  We normally do not know this. Even with chamber pressure values from a pressure gun, and approximate muzzle pressure.  I am also not certain what time element would be used in determining the mass flow rate.

 

Thereby, historically, any jet effect adding to recoil is ignored.

[Tango]

In the OP I gave exact numbers from the Speer lawman line and compared 115 to 147 grain. The heavier Speer has more physical recoil but does feel "softer". I think this is all psychological: shooters reacting to supersonic blast and "feel" it is recoiling more.

[ima45dv8]

That is an interesting theory.

I don't think there's any validity to it, but it is creative.

[12glocks]

I think the fast burning propellants associated with action shooting having a perceived softer recoil impulse.  Consider shooting  a 147 loaded to the same velocity with Power Pistol and a faster propellant like N320, Red Dot, or Titegroup.  I have done this and the faster propellants seem softer and they lock the slide back more reliably.  I shot around 20K or so rounds of handloaded 147s and tried factory 115s.  There was a marked difference in my opinion.  Yes, I know PF is not equivalent there.

[broadside72]

Isn't this is a simple case of the laws of physics and the blowback design of most pistols? The less powerful force of the lower powder charge for heavier bullets (for same PF) means that the bullet is moving slower and the case has less rearward force/speed on the breech face so the slide moves slower, thus the "push" vs the "snap" feeling. That pesky equal and opposite force thing....

[GBertolet]

The muzzle energies of 115 gr bullet and the 147 bullet are not even close when loaded to the same power factor. The foot pounds of energy are considerably less with the heavier bullet, even though the power factors are the same. Pick any caliber, and bullet weights to compare, and compute what velocity is needed to make power factor. Go to a ballistics chart, and see what the energy is for those bullet weights, and compare. The heavier bullets are less powerful, energy wise. This will explain why heavier bullets recoil less. You get to choose your poison. Heavy bullets=slower cycling, and light bullets= faster cycling.  In revolvers, the heavier bullets really shine, as there is no sluggish reciprocating slide.

[Tango]

1 hour ago, GBertolet said:

The muzzle energies of 115 gr bullet and the 147 bullet are not even close when loaded to the same power factor. The foot pounds of energy are considerably less with the heavier bullet, even though the power factors are the same. Pick any caliber, and bullet weights to compare, and compute what velocity is needed to make power factor. Go to a ballistics chart, and see what the energy is for those bullet weights, and compare. The heavier bullets are less powerful, energy wise. This will explain why heavier bullets recoil less. You get to choose your poison. Heavy bullets=slower cycling, and light bullets= faster cycling.  In revolvers, the heavier bullets really shine, as there is no sluggish reciprocating slide.

"Pick any caliber, and bullet weights to compare, and compute " 

 

That is exactly what i did in the OP

[Umbrarian]

On 6/22/2021 at 8:38 PM, Tango said:

When I was a beginner and shooting only factory ammo, I was told to stay away from lighter bullet weights like 115gr, and use 147gr because heavier rounds would recoil lighter. My experience confirmed this: 147gr rounds felt better and easier to control. Physics, however, tells us that recoil is momentum, and a heavier bullet at the same speed would generate larger recoil. So I compared momentum of a typical factory ammo like Speer lawman, at 115 and 147 grains. Based on factory specs, the momentum of the 147gr is actually larger than the 115gr, but by only about 5%. I do not think anybody can notice this difference in their hand, but even if they do, the heavier bullet should recoil more. This is contrary to what people feel. What I believe happens is that because the 115 grain bullet is actually supersonic, it creates blast that makes it feel more "snappy" vs. 147 grain is subsonic and doesnt create the same shock wave and the perceived snappiness. 

No, recoil is Force (F=ma), not momentum (p=mv).

 

Unless you are shooting a revolver, what you feel is also a result of the Recoil Spring absorbing energy.

 

Supersonic bullets do not create more blast. 115 seem to have more blast over 147 as more powder is used.

[Guy Neill]

Recoil is historically reported as the kinetic energy of the gun.

 

Reference:

 

Hatcher's Notebook

 

SAAMI (as taken from the British Textbook of Small Arms 1929)

[SGT_Schultz]

On 6/24/2021 at 12:39 PM, broadside72 said:

Isn't this is a simple case of the laws of physics and the blowback design of most pistols? The less powerful force of the lower powder charge for heavier bullets (for same PF) means that the bullet is moving slower and the case has less rearward force/speed on the breech face so the slide moves slower, thus the "push" vs the "snap" feeling. That pesky equal and opposite force thing....

That's not how conservation of momentum or energy works

Edited June 27, 2021 by SGT_Schultz

[SGT_Schultz]

On 6/25/2021 at 5:09 PM, Umbrarian said:

No, recoil is Force (F=ma), not momentum (p=mv).

 

Unless you are shooting a revolver, what you feel is also a result of the Recoil Spring absorbing energy.

 

Supersonic bullets do not create more blast. 115 seem to have more blast over 147 as more powder is used.

 

More to the point, kinetic energy (which is what a recoiling pistol imparts on your hands) is mass times the square of the velocity of the mass.

 

 

[Tango]

On 6/25/2021 at 4:09 PM, Umbrarian said:

No, recoil is Force (F=ma), not momentum (p=mv).

 

Unless you are shooting a revolver, what you feel is also a result of the Recoil Spring absorbing energy.

 

Supersonic bullets do not create more blast. 115 seem to have more blast over 147 as more powder is used.

No, recoil is momentum. No, supersonic bullets create a supersonic shock wave, subsonics don't do that. I agree though, generally the total energy (i.e. powder) is a better measure of "felt recoil". 

Edited June 27, 2021 by Tango

[Umbrarian]

8 hours ago, Tango said:

No, recoil is momentum. No, supersonic bullets create a supersonic shock wave, subsonics don't do that. I agree though, generally the total energy (i.e. powder) is a better measure of "felt recoil". 

Not according to Isaac Newton, who discovered it. Recoil is exactly Newton's 2nd & 3rd Laws in action. I think your misunderstanding here is that recoil is an example of momentum being conserved, but it is not momentum itself. Newton's 3rd law relies on conservation of momentum to work.

 

Correct, supersonic bullets can create shock waves, and subsonic dont, but that was not what you asked/said "What I believe happens is that because the 115 grain bullet is actually supersonic, it creates blast". So no, it does not create blast or more blast or have anything to do with blast.

 

Edited June 27, 2021 by Umbrarian

[Umbrarian]

21 hours ago, SGT_Schultz said:

 

More to the point, kinetic energy (which is what a recoiling pistol imparts on your hands) is mass times the square of the velocity of the mass.

 

 

 

Yes since "recoil" is not part of classical Newtonian physics, there is more ways to define than just Newtons - N (Raw Force),  N*s (impulse), velocity (m/s), joules (energy). I usually go with "Recoil Force", measured in Newtons, but "Recoil Energy" measured in ft-lbs or joules is also fine.

Edited June 27, 2021 by Umbrarian

[superdude]

A couple things. . . 

 

If bullets of different weights are pushed to the same power factor with the same powder, the lighter bullets will produce more recoil force. 

 

Light bullets must go faster than heavy bullets to achieve the same power factor, so they accelerate faster and spend less time in the barrel. This means a faster recoil impulse. The light bullets' shorter barrel time and additional recoil likely combine to make their recoil feel different from heavy bullets. 

 

Source:  https://www.shootingtimes.com/editorial/power-factor-recoil-bullet-weight-gives-edge/99399