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1,287 Posts
...As to kinetic energy, velocity has a lot more impact than mass. Mass is linear and velocity is squared...

There may well be some truth here. Shooting .38 Special and 9mm Smith Centennials back to back, the nine has a much sharper recoil. The bullets are 148 gr and 115gr respectively, but the nines are crowding 1100, while the .38s are less than 800. I haven't done the energy math, and there are other variables, but the quick jump to 1100'sec has to make a difference.
The kinetic energy formula is:

Ke = 1/2 Mass x Velocity ^2

So yes....speed impacts energy a lot more than weight.

817 Posts
Power factor relates to the momentum transfer which is really the key physics characteristic in recoil and displacement.
Mass in (grains) multiply by velocity divide by 1000. Use unitless factor.

PF =( m *v)/1000

Note even the term " power factor" is vague (slang) because the dimensions of the PF equation are the physics units for momentum p. P=m*v. Mass time velocity.

To show how "wrong or incorrect descriptive term power factor equation is relative to the correct physics terms:
Physics definition of power is power =work/time
Work = force applied over distance W =F*d
and F =Mass time acceleration F=ma. Famous Newton equation for Force.
Acceleration is
a = velocity/time.

But look at the dimensions of the given USPSA PF , really momentum transfer correlation.
As a quick and easy correlation the PF equation is a usefull figure of merit
Da as everyone does let's use the USPSA correlation PF.

Set the same PF to compare two loads say 9 mm 147 gr and 115 gr.

So the different loads , the mass and the velocity can be adjusted by the loader to get the same power factor.

So say for a 9 mm load.
The 147 gr will have a slower velocity than a 115 gr at the same power factor.

This is why the 115 gr 9 mm will feel more snappy than a 147 for the same power factor.

The 115 gr faster velocity also have greater acceleration and shorter transit time in the barrel.
, but momentum is key parameter.

So the same momentum transfer happens more quickly and the felt recoil will be more pronounced for thev115 gr load.

Could also think of impulse as the force applied in a time interval.
The slower bullet will apply the same momentum transfer over a longer time duration so the recoil is a push rather than a punch of the lighter bullet applied over a shorter time.

The reactive force of the gun comes into play too as the slide and entire gun will have the momentum transfer.

Why each gun PPS vs ppq is felt differently would be how the different slide weight lock time, offset from grip distance angle etc react to the momentum transfer from the cartridge bullet reaction.

It would have been better for the USPSA to call the PF by a better name such as momentum factor.
But hey gun professionals talk about knock down power too.

14 Posts
I'm a fairly new shooter and bought a (polymer frame) Q5 as my first non-22 pistol. It's just a range gun for fun and I'm happy with it.

I recently rented a PPS (M2) and I was surprised to find that it felt like it had less recoil, or maybe I should more properly say muzzle flip, than my Q5. I expected it to be worse, given how small it was, but it wasn't.

My theories as to why:
  1. I haven't done any measurements, but it seems like the bore axis on the PPS is maybe a little lower than the Q5. It looks like just barely though, and I wouldn't expect this to offset the weight advantage that much.
  2. Newton's law basically. If the bullets are slower coming out of a shorter barrel because some gas escapes, then lesser force must be exerted on the bullet and therefore lesser force must exerted the opposite direction on the gun. That said, I thought the drop in 9mm bullet velocity between 3" and 5" wasn't that much, like 10% on average. Could I really perceive that recoil reduction?
  3. I'm a shorter guy with smaller hands. While the Q5 doesn't feel too big in my hands, I can get a much tighter grip on the thin little PPS.
  4. It's entirely psychosomatic. I shot around 50 rounds through the PPS before picking up my Q5 and maybe it was just wrist fatigue already setting in. Although I'll usually go through 150 rounds of 9mm in a range session before I'll noticeably feel wrist fatigue and my aim suffers.
Has anyone else noticed the same or has enough knowledge to corroborate one of my theories?

Regardless of all that I really liked the PPS except that my trigger finger uncomfortably rubbed on the edge of the cut out section at the bottom of the trigger guard (a commonly reported problem I see) and I had to really concentrate to not ride the bottom of the trigger.
You are on to something. I havde a few 44 magnum revolvers. A 6 1/2 inch barrel, and a 10 1/2 inch barrel I used as a hunting handgun. The longer barrel creates more muzzle energy. It, also has more felt recoil and flip shooting the same rounds. Try torquing your wrist down on your trigger finger hand, like you are inserting the gas pump nozzle into your car. High up on the grip to the slide. This bent wrist along with a grip that slightly feels like you are tightening a quart jar lid .. Elbows slightly bent. This will make the gun, hands, forearms and upper arms a one unit triangle. Recoil will raise everything in that triangle greatly reducing recoil, muzzle flip, instead of just the wrists only. Do this only to see every part of this will nearly eliminate flip. You can use this to learn how to spread out the effect of recoil and flip over the triangle instead of just the the wrists. You may not be able to shoot well this way, but you will see how making the whole triangle absorb recoil. Go from there and adjust to your liking. its really a little of all of those elements that controls the recoil. The jar twist replaces the old push pull grip. It is amazing. I was shooting my friends 1911 10mm. He could not believe how I could control his 10mm with minimus rise. It is the difference of swinging a hammer with the wrists only as opposed to using both arms and hands. The downward resistance is more tham quadrurpled

113 Posts
This is a simple question for those who have studied the "theory of mechanisms and machinery".
The recoil is generated by the recoil momentum of the cartridge. This is so, but only indirectly, the rest of the billiard.

FEELING recoil, including the jump, mainly determines the momentum of the slider when it hits at the end of the rollback.
The lighter the slider (and its lower the speed), the less the momentum of the entire gun.
Similarly, the height of the axis of the barrel affects the feeling of recoil only indirectly. And apart from the rest of the design does not make sense.
Determining is the height of the center of gravity of the moving parts and the height of the fulcrum of the return spring.
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