115gr vs 124gr vs 147gr felt recoil

[Lemming]

A fundamental truth is that momentum is conserved. In other words,  the system starts at rest with zero momentum - so it must have zero net momentum after firing. This happens because the momentum of the stuff going forward (bullet plus gas) exactly equals the momentum of the stuff going backwards (the recoiling gun / hands).

Given the big mass of the bullet (relatively) and the small mass of the gas, I expect that the gas momentum is negligible.  So I'm afraid I disagree with you on that point,  1SOW.

At the same power factor (momentum) all bullet weights will have the same recoil momentum. What differs is time and hence impulse

The only time the momentum transfer (force) can happen is while the bullet is in the barrel. This is shorter for light bullets at higher velocities, so the force required to transfer the same momentum in a shorter time is higher  - hence more felt recoil.

[Smitty79]

A fundamental truth is that momentum is conserved. In other words,  the system starts at rest with zero momentum - so it must have zero net momentum after firing. This happens because the momentum of the stuff going forward (bullet plus gas) exactly equals the momentum of the stuff going backwards (the recoiling gun / hands).

Given the big mass of the bullet (relatively) and the small mass of the gas, I expect that the gas momentum is negligible.  So I'm afraid I disagree with you on that point,  1SOW.

At the same power factor (momentum) all bullet weights will have the same recoil momentum. What differs is time and hence impulse

The only time the momentum transfer (force) can happen is while the bullet is in the barrel. This is shorter for light bullets at higher velocities, so the force required to transfer the same momentum in a shorter time is higher  - hence more felt recoil.

I don't buy this model.    I think it's all about the kinetic energy imparted to the bullet.   I believe sensed recoil is more about average force than peak force.   The residence time of the bullet in the barrel is about a millisecond (average velocity is half of muzzle velocity and the barrel is 6in long).   The human mind can't detect the force change over time for that.   It just integrates over the time to know the hand has been pushed.   Since average force times distance is energy and the muzzle energy of a bigger bullet is lower, the average force is lower, hence the sensed recoil is lower.    For pistol rounds, looking across different powders at constant bullet and muzzle velocity, the powder with the lower charge mass has less stuff coming out the barrel and should be softer.   This should be a smaller effect than bullet mass.

[Lemming]

I guess I should complain about my engineering degrees then if they're teaching us crap [emoji1]

[1SOW]

Lemming,  you aren't hearing that from me.  I respect the science.  I also believe the results of tests.

Visualize a test.   Anchor a pistol rigidly and connect it to a force transducer to measure the maximum force --straight back,  as flip is eliminated with the mount.>  The force transducer is mounted in a direct line behind the bbl.  This is to eliminate the affect of the "felt recoil" subject to pistol design.
The only factor being measured is the resultant force straight back

With the givens,  fire a 115 gr bullet with an example 8 grains of powder to achieve the speed needed to reach the power factor..
Now fire a 124 gr bullet with 6 grains of powder (may not be proportionate, but works as a sample) to achieve the speed needed.
Finally,  fire a 147 gr bullet with 4 grs of powder to attain the speed needed.

My finding empirically is that the recoil is inversely proportionate to the bullet weight AS IS THE POWDER WEIGHT. 
Adding to the bullet mass doesn't change the power of the ONLY "ENGINE" that drives it--THE POWDER LOAD's  gas quantity and pressure generated.

With one actual example of where this doesn't hold true,  I'll learn and agree to another 'truth'.

Something(s) in the math model is missing.   Probably from my ignorance of the physics involved.
 

[Lemming]

1SOW - I think we are in agreement but are just conceptualising it slightly differently.

As bullet weight goes down (at a fixed power factor), the velocity goes up. This means the bullet spends less time in the barrel,  so you need a bigger bang (more powder - more force) to get it up to speed in a shorter time.

So yes - recoil goes up as the powder charge goes up. This is what your test demonstrates.

That is just another way of saying the impulse force has gone up. Impulse is force multiplied by time. Since the barrel time is shorter,  the force is greater. The way we get this extra force is to use more powder.

We are really saying the same thing. ....

I'm just doing it from a momentum transfer point of view and you are using experimental methods

[Lemming]

Smitty79, it is certainly possible to analyse the situation using the conservation of energy as a basis. But then you need to include the energy turned into light,  heat and sound - and the energy involved with the chemical compounds produced by combustion. You would need to look at turbulence,  friction, etc. It gets real ugly real fast.

I am afraid I'm not brave enough to attempt the maths on that one. ...[emoji1]

The conservation of momentum is often much simpler,  which is why engineers like to use it.

[Towns]

Maybe it's because I had a busy day at work.............but you guys are making my brain hurt.

[Smitty79]

Smitty79, it is certainly possible to analyse the situation using the conservation of energy as a basis. But then you need to include the energy turned into light,  heat and sound - and the energy involved with the chemical compounds produced by combustion. You would need to look at turbulence,  friction, etc. It gets real ugly real fast.

I am afraid I'm not brave enough to attempt the maths on that one. ...[emoji1]

The conservation of momentum is often much simpler,  which is why engineers like to use it.

Those extra things are all second order effects.  Kind of like the second order term in the expansion of 1/(1-x) where x<<1.  If I remembered my perturbation theory, I could take a stab at it.   On the other hand, unless you hold bullet weight and muzzle velocity constant, excepting Saint Miculek, no one is sensitive to detect them anyway.

[IDescribe]

All right, physicists.  Here is your word problem.

 You have just bought a new gun. The light recoiling 124gr bullet at 130 PF that you have been shooting in competitions will only cycle the slide and eject the spent case about 95% of the time with the new gun. You know this is because the recoil spring on the new gun is slightly heavier than your production gun. If you wanted to shoot the same type of gunpowder at the same power factor with the same recoil spring, would a 147gr bullet or 115gr bullet loaded to 130PF with same powder be more likely to cycle the slide 100% of the time.  And why?

[Smitty79]

Smaller bullet.   Spring needs extra energy to cycle all the way.   Lighter bullet load has more powder to produce that energy.

[Riptide439]

Never took physics guys but logic tells me the load with more powder would produce more gas hence causing more reaction to push the slide back. I would say the 115grn bullet would cycle better since it takes more powder to get it going to hit the velocity needed.

Larger bullets are the opposite - less powder, less gas, less recoil - harder for the slide to cycle.

[1SOW]

Buy that man a beer. 

[IDescribe]

Now let me throw a shoe into the gears.  Factoring in that the bullet is somewhere between almost out of the barrel and all the way out of the barrel before the slide even moves -- does the 147gr bullet get any extra credit for the greater dwell time in the barrel? 

[Smitty79]

Now let me throw a shoe into the gears.  Factoring in that the bullet is somewhere between almost out of the barrel and all the way out of the barrel before the slide even moves -- does the 147gr bullet get any extra credit for the greater dwell time in the barrel? 

I don't know, but I doubt it.  In fact, the slide starts moving at essentially the same time as the bullet.   It hasn't moved very far yet, but it's started.   The transfer of energy to the gun to get the slide moving is essentially over when the bullet and combustion gasses leave the barrel.   This would be the point of peak velocity.   From there, friction and the recoil spring are slowing the slide down.

[jameslovesjammie]

I don't know, but I doubt it.  In fact, the slide starts moving at essentially the same time as the bullet.   It hasn't moved very far yet, but it's started.   The transfer of energy to the gun to get the slide moving is essentially over when the bullet and combustion gasses leave the barrel.   This would be the point of peak velocity.   From there, friction and the recoil spring are slowing the slide down.

Visuals:

https://www.youtube.com/watch?v=ySO0EWIlOKc

Never took physics guys but logic tells me the load with more powder would produce more gas hence causing more reaction to push the slide back. I would say the 115grn bullet would cycle better since it takes more powder to get it going to hit the velocity needed.

So if this is true, then what happens when you have two loads at the same powder factor with the SAME bullet weight, but one using 3.7 grains of powder A and one using 4.3 grains of powder B?  The 3.7 grains is a max load at 32,500 CUP and the 4.3 grain load is a starting load at 28,900 CUP?  Will the 4.3 grain load recoil more even though less pressure is generated?