Bullet weight vs. speed vs. felt recoil

First topic message reminder :

I'm trying to understand the relationship between bullet weight, bullet speed, the gun that is being used, and felt recoil.

For example, I used to shoot 115gr ammo in my Taurus PT9 "stock" handgun, and while I can't say the gun had a lot of recoil, what it did have was annoying.  User 'mustachio' suggested I try the heavier 147 gr ammo, which I found easier to shoot.  Less "felt recoil.

I know there's the mathematical equation of combining weight and speed.  All other things being equal, the heavier round should create more recoil.
I know the bullet speed is part of this, with the 115gr round being supersonic, while the heavier load is sub-sonic.

Since I'm referring to "felt recoil", there probably isn't any way to actually calculate that....??


My question.  Is it possible, using the data that can be found in reloading charts, to compare the expected recoil between two different rounds?

(.....and for a test, does this show the decrease in felt recoil in my 9mm gun, when switching from 115gr ammo to 147gr? )

Wobbley wrote:How it “feels” is somewhat ( maybe significantly) subjective.  

However, these concepts may help.

Recoil is a momentum exercise.  The momentum of the gun has to match the momentum of the bullet.  So MgVg = MbVb

So a 147 grain bullet at 920 fps has the same momentum as a 115 at 1175 fps.  Those are about max loads in a 9mm.  Both will impart the same recoil velocity to the gun.  The recoil energy is the same.  The difference is the time.  The bullet is accelerated from rest to muzzle velocity in the same distance, the same peak pressure is reached.  But the overall acceleration has to be different.  The 147 grain bullet takes .00045 seconds to leave the muzzle.  The 115 takes .00035 seconds.  So the MEAN force to accelerate the pistol to the end velocity has to be higher.  This means the mean force is about 30% higher for the 115 load.  That will be perceptible.  

In my limited experience with this, it's easier to download heavier bullets to low momentum than lighter bullets, AND get the gun to function reliably.

I load 147 gr bullets to about 750 fps with N310 and it's extremely soft shooting.

Wobbley wrote:
So a 147 grain bullet at 920 fps has the same momentum as a 115 at 1175 fps.  Those are about max loads in a 9mm.  Both will impart the same recoil velocity to the gun.  The recoil energy is the same.  

The recoil velocity of those two loads is not the same. Close maybe, but not the same according to my calculations. 

Same thing for the recoil energy. Not the same, but close. 

you can confirm at http://kwk.us/recoil.html

Wobbley wrote:How it “feels” is somewhat ( maybe significantly) subjective.  

However, these concepts may help.

Recoil is a momentum exercise.  The momentum of the gun has to match the momentum of the bullet.  So MgVg = MbVb

So a 147 grain bullet at 920 fps has the same momentum as a 115 at 1175 fps.  Those are about max loads in a 9mm.  Both will impart the same recoil velocity to the gun.  The recoil energy is the same.  The difference is the time.  The bullet is accelerated from rest to muzzle velocity in the same distance, the same peak pressure is reached.  But the overall acceleration has to be different.  The 147 grain bullet takes .00045 seconds to leave the muzzle.  The 115 takes .00035 seconds.  So the MEAN force to accelerate the pistol to the end velocity has to be higher.  This means the mean force is about 30% higher for the 115 load.  That will be perceptible.  

Thus the heavier bullet moving slower has less felt recoil.

Wobbley wrote:........This means the mean force is about 30% higher for the 115 load.  That will be perceptible.  

I'm struggling to follow all the math and formulas, but the TIME factor makes sense.  The 115 seems more "snappy", which matches what you've written.  The 147 grain bullet might even produce more actual recoil, but it doesn't "feel" as annoying.

I never enjoyed shooting my 9mm Taurus with the 115gr ammo.  The 147gr ammo seems to make it more comfortable/enjoyable....  not sure what the correct word would be.   Mustachio is the one who suggested this, and I followed his advice.

mikemyers wrote:

Wobbley wrote:........This means the mean force is about 30% higher for the 115 load.  That will be perceptible.  

I'm struggling to follow all the math and formulas, but the TIME factor makes sense.  The 115 seems more "snappy", which matches what you've written.  The 147 grain bullet might even produce more actual recoil, but it doesn't "feel" as annoying.

I never enjoyed shooting my 9mm Taurus with the 115gr ammo.  The 147gr ammo seems to make it more comfortable/enjoyable....  not sure what the correct word would be.   Mustachio is the one who suggested this, and I followed his advice.

If I'm interpreting Wobbley's post correctly, there is some confusion.  Wobbley appears to be getting the 30% value from the time measurement.  That only applies to time.  Time does not equal recoil force. They are two different things.

Let's just lay out the numbers here to prevent any more confusion.  Let's plug Wobbley's numbers into a formula that calculates recoil force. I have included estimates of how much gunpowder it takes to push a bullet to his speeds. The gunpowder weight adds to the recoil force and is required for the most accurate estimate. I used data from Hornady's manual with Power Pistol gunpowder in a 9mm. I used a 2 pound gun for the calculation. 

115 gr @ 1175 fps.   
6.2 gr Power Pistol
power factor = 135
Muzzle energy = 352 ft lbs
recoil velocity = 10.43 fps
recoil force = 3.38 ft lbs

147 gr @ 920 fps.
4.6 gr Power Pistol
power factor = 135
Muzzle energy = 276 ft lbs
recoil velocity = 10.11 fps
recoil force = 3.18 ft lbs

The numbers to compare are in bold.  The 115 grain bullet produces 3.38 ft lbs of recoil force, the 147 grain bullet produces 3.18 ft lbs of recoil force.

3.38 / 3.18 = 1.0628  The 115 grain bullet produces 6.3% more recoil than the 147 grain bullet when pushed to the same power factor.


There is a 6% difference in recoil force. That's the number to focus on when looking at differences in recoil.  If you want to know the difference in recoil, measure recoil. Don't measure something else and think it is a substitute for recoil. 


Barrel time matters and can account for the light bullets feeling 'snappier' because they have to accelerate faster to reach their faster speed. That's why heavier bullets at the same power factor feel 'softer'. They don't have to accelerate as fast because they have a lower exit velocity. That leaves heavy bullets more time for barrel travel so they don't hit you as quick. 

In conclusion, light bullets accelerate faster AND produce more recoil force (at the same power factor as heavy bullets).

I will say this for the third time, if you want to understand the relationship between bullets of different weights pushed to the same power factor, read the link below. It is explained, calculated and measured/demonstrated with live ammo in a 45 Auto.  That is the whole purpose of that article. 

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

I hope this helps.

Some confusion can result from definitions and use of terms.  Power Factor is a momentum calculation, while free recoil is often expressed as a kinetic energy calculation.

A take home note:  If your main effort is to reduce recoil, use the least volume of powder that gives you the requisite velocity.

(Edit) Another note, if you want to reduce recoil, to paraphrase Roy Scheider "I think you're going to need a bigger gun..."

Now - back to your pencils and paper, and be sure to show your work on the quiz 

Just scored a guy shooting 885-32x in our league last night.
Asked him if he worried about this in his process.

S148 wrote:..........Barrel time matters and can account for the light bullets feeling 'snappier' because they have to accelerate faster to reach their faster speed. That's why heavier bullets at the same power factor feel 'softer'. They don't have to accelerate as fast because they have a lower exit velocity. That leaves heavy bullets more time for barrel travel so they don't hit you as quick..........

Again, I suspect this is the answer as to why I enjoy shooting 147 more than 115.   

(I can't add more or less powder, as they are all purchased.)

I find the explanation fascinating, but maybe what I'm talking about is "bullet weight", not "recoil".

I think an analogy would be if one of you were to:

• slap me in the face or
  
• "push" my face over a duration of one second, applying the same total force. 
  

In the first case, it would hurt.  In the second it would merely be a little annoying.

Thank you all for sorting this out.

115 gr @ 1175 fps.
6.2 gr Power Pistol
power factor = 135
Muzzle energy = 352 ft lbs
recoil velocity = 10.43 fps
recoil force = 3.38 ft lbs

147 gr @ 920 fps.
4.6 gr Power Pistol
power factor = 135
Muzzle energy = 276 ft lbs
recoil velocity = 10.11 fps
recoil force = 3.18 ft lbs

Ft-lbs is a measure of energy not force.

Force is measured in pounds.

Since the gun has to accelerate to the same velocity over two time periods, the force has to be higher in the shorter time.

Based on this total discussion, my advice to mikemyers was sound.

Sure was!  "Sound" is an understatement.  It changed the Taurus from something I didn't really enjoy shooting, to something I'm comfortable with.

The formulas, etc., are fascinating, and I enjoy trying to understand them, but to me it's far more important to get the gun to feel better in MY hands.  


(Due to an unplanned issue --bolt pin on Model 41 snapped in two-- I don't have time to get anything else ready for a match tomorrow.  I can either take the Taurus, which is all set, or my M-52 which hasn't been used in over a year.  Minimal practice time.  I'm likely to go with the Taurus, or possibly shoot both and see which is working better for me.)

I am putting a red dot on my Beretta and will try it for centerfire matches with 147 gr. Using iron sights it is right on, I can only hope for better with the red dot. 
Where are you shooting for tomorrow's match?

I didn't see this in time to answer, but the club is the Hollywood Rifle and Pistol Club.   Address, etc;, is here:

Hollywood Rifle and Pistol Club
2989 Stirling Road
Dania Beach, Fl 33312

https://www.google.com/maps/place/2989+Stirling+Rd,+Fort+Lauderdale,+FL+33312/@26.048301,-80.182471,15z/data=!4m5!3m4!1s0x88d9aa26075f5c9b:0xaa014aed09a498b8!8m2!3d26.0480113!4d-80.181943?hl=en

If you want to come, next Sunday will be much more exciting:
http://hrpclub.info/26.html

They are expecting a lot of shooters, and the "rifle side" of the club may be shut down, so there may be two "relays" to deal with all the shooters.

what type of match?

mustachio wrote:what type of match?

DATES AND STARTING TIME:  Match is held quarterly, on the last Sunday of any month with five Sundays.  Firing commences at 1000 (10:00 AM).
NOTE:  It is recommended that shooters bring a staple gun for posting targets, pen or pencil for keeping score, and “pasters” (black, and beige or white) to repair targets.

SCORING:  Targets are scored by competitors.  Competitors may use a plug type scoring gauge and/or overlay.  Once a plus is inserted in a shot hole, it is not to be removed until a decision on the shot value is determined.  If competitors cannot agree, the Match Director or designee makes the decision, which is final
TARGETS:  NRA B-8    
SIGHTING SHOTS:  Unlimited sighting shots – time limit at the discretion of the Match Director

mustachio wrote:what type of match?

If you come in one more month, you can join the "Bullseye Group".
Feel free to bring your friends.  
It's not a full match, but it is similar, and is lots of fun, and when it's 95 degrees outside, people are glad to get into the A/C clubhouse when it's over.



TARGETS:  NRA B-8                       TOTAL POSSIBLE SCORE:  900-90x
COURSE OF FIRE:  Florida Peace Officer’s Short Course

BULLSEYE MATCH:  A modified 90 round Bullseye match is available. This match consists of one-handed shooting at 25 and 50 yards. 

Note - I haven't yet installed the adjustable sight you recommended on my Taurus.  Today I used the S&W Model 52.  If I get the Taurus set up for next time, I'd like to see how it does.

This ties into the discussion, in that I never even considered bringing the Taurus when all I had was the 115gr ammo.  With the 147 gr ammo I was prepared to shoot it today.  Now it's an enjoyable gun to shoot, with the heavier rounds.

A side-note.  The Taurus is aluminum, and very light.  I suspect if I buy a 1911 made for 9mm, I will enjoy it a lot more than the Taurus. 

If a 9mm 1911 showed up in the "Commercial Row", I'm not sure I could resist..............



Also, I'm wondering if someone who understands the formulas that have been posted better than I do, could copy them to a new thread that could be made into a "sticky".  There's a lot of good information here that people in the future would probably never find.