Question about perceived recoil

[Old Scatterbrain]

Which is a better indicator of perceived recoil, momentum or energy?

 

Momentum, of which power factor is a representation, is a product of mass and velocity. Energy is a product of mass and velocity squared.

 

Cartridge A is loaded with a 180-grain bullet which leaves the muzzle at 834 feet per second, for a power factor of 150. Cartridge 2 propels a 250-grain projectile at 600fps, resulting again in a PF of 150. However, cartridge A will produce nearly 40% more muzzle energy than cartridge 2. Will it produce more recoil, or should recoil be perceived as the same?

[Pulp, SASS#28319]

Well, I ain't one of those fellers what can scribble a whole bunch of funny lookin' letters on a chalk board and come up with whatever who's payin' the most wants to hear, but based on what you're sayin', actual recoil should be close to the same.

 

Perceived recoil is a different animal. If one of the loads uses TiteGroup powder, which has a sharper and louder report, folks will say that load kicks harder. Or if one of the loads produces a big fireball compared to the other, folks will say it kicks harder.

[Old Scatterbrain]

Well, I ain't one of those fellers what can scribble a whole bunch of funny lookin' letters on a chalk board and come up with whatever who's payin' the most wants to hear, but based on what you're sayin', actual recoil should be close to the same.

 

Perceived recoil is a different animal. If one of the loads uses TiteGroup powder, which has a sharper and louder report, folks will say that load kicks harder. Or if one of the loads produces a big fireball compared to the other, folks will say it kicks harder.

Yes, there are alot of other variables which I basically am ignoring for the question.

[Subdeacon Joe]

My gut feeling is that the faster load will give a sharper perceived recoil, more of a snap, and the slower will give a healthy push.

 

I find a moderate factory loaded .40 S&W out of a Glock much more unpleasant than a hot hand loaded .44 Mag out of any reasonably sized handgun.

[Forty Rod SASS 3935]

The best indicator of perceived recoil is the pain caused to the shooter. I know a man who is terrified of a .30-30 model 94 carbine's recoil but frequently shoots a 7mm Rem Mag, a .375 H&H, and a .45-120 Sharps. He swears the .30-30 kicks "harder" and hurts worse that any other gun he owns.

 

It could be a matter of geometry, too. He's 6'4" and weighs about 175 pounds. The 7mm and the .375 are both custom stocked.

[Old Scatterbrain]

The best indicator of perceived recoil is the pain caused to the shooter. I know a man who is terrified of a .30-30 model 94 carbine's recoil but frequently shoots a 7mm Rem Mag, a .375 H&H, and a .45-120 Sharps. He swears the .30-30 kicks "harder" and hurts worse that any other gun he owns.

 

It could be a matter of geometry, too. He's 6'4" and weighs about 175 pounds. The 7mm and the .375 are both custom stocked.

Comparing weapons of different weights with differently-shaped buttstocks or grips doesn't tell you much about the difference in the recoil produced by the various cartridges. I also dislike the .30-30 model 94 because it kicks too hard, but I have much less difficulty shooting an M14, for example.

[J-BAR #18287]

Recoil is a function of momentum (mass times velocity), not energy (mass times velocity squared).

 

When firing a gun, momentum is conserved, not energy. The MXV of the projectile and gasses and unburned powder going forward is the same as the MXV of the gun going backwards (recoiling).

 

If energy were conserved the handgun would hit your hand with the same force (kinetic energy) that the bullet hits the target. You would not like it.

 

In the example you gave, it's nearly a dead heat. The 180/834 generates a tiny tad more momentum than the 250/600. I doubt you could perceive the difference.

 

Why don't you try it and see. Make it a double blind test so you don't know which load you are firing and let us know.

[Old Scatterbrain]

Recoil is a function of momentum (mass times velocity), not energy (mass times velocity squared).

 

When firing a gun, momentum is conserved, not energy. The MXV of the projectile and gasses and unburned powder going forward is the same as the MXV of the gun going backwards (recoiling).

 

If energy were conserved the handgun would hit your hand with the same force (kinetic energy) that the bullet hits the target. You would not like it.

Why, as in how, is energy not conserved?

 

In the example you gave, it's nearly a dead heat. The 180/834 generates a tiny tad more momentum than the 250/600. I doubt you could perceive the difference.

I did that intentionally. There would be less than 0.1 percent difference, statistically insignificant.

 

Why don't you try it and see. Make it a double blind test so you don't know which load you are firing and let us know.

I don't have a chronograph, nor any way to measure the recoil (energy or momentum), plus a host of lesser reasons.

 

Actually, I should have known the answer, but it has been along time since 10th grade physics class, and 22 years in the military tends to dull one's intellect.

[Noz]

Come on guys!

Perceived recoil is a subjective thing and not subject to interpretation.

It simply is how much recoil did YOU feel.

Was it more or less?

Cannot be quantified except in your own mind.

[Forty Rod SASS 3935]

Comparing weapons of different weights with differently-shaped buttstocks or grips doesn't tell you much about the difference in the recoil produced by the various cartridges. I also dislike the .30-30 model 94 because it kicks too hard, but I have much less difficulty shooting an M14, for example.

 

But we are discussing "perceived" recoil Perception is in the shoulder of the shooter...and his mind...and can't always be calculated reasonably.

[J-BAR #18287]

"why is it momentum and not energy?"

 

Physics answers "how much", not "why."

 

You do the experiment, make the measurements under controlled laboratory conditions, and you find that the momentum of the bullet is the same as the momentum of the gun in the opposite direction. It's called a "law" of physics because you get the same answer each time the experiment is performed. In this case, it is Newton's first law of motion.

 

Total mass and energy of the system IS conserved. No mass is created or destroyed since it is not a nuclear reaction. The chemical energy stored in the gunpowder is converted into heat energy and kinetic energy of the expanding gasses, the bullet, and the recoiling gun. So the total energy of the system is the same before and after the gun is fired, but not kinetic energy.

 

"Why" is philosophy, not physics. Some go to church for those answers.

[Old Scatterbrain]

"why is it momentum and not energy?"

 

Physics answers "how much", not "why."

There has to be an answer to "why this formula, and not that formula".

 

You do the experiment, make the measurements under controlled laboratory conditions, and you find that the momentum of the bullet is the same as the momentum of the gun in the opposite direction. It's called a "law" of physics because you get the same answer each time the experiment is performed. In this case, it is Newton's first law of motion.

The first law deals with inertia, but I think my question has more to do with the third law- the cliche of equal and opposite reactions.

 

Perhaps you can review this and either quote or maybe rephrase the pertinent section, which might light the bulb in my head.

 

"Why" is philosophy, not physics. Some go to church for those answers.

Uh, what?

[Charlie Harley, #14153]

The 7mm and the .375 are both custom stocked.

 

Forty hit the nail on the head. We can talk physics, momentum, energy, PF, and everything scientific until the cows come home. Those are not the big issue that matters in perceived recoil.

 

A properly fitted stock will spread the recoil evenly over the shooter's shoulder and bone structure. That eliminates pressure points which cause pain to the shooter. Pain increases his/her perceived recoil.

 

A loud muzzle blast will hurt the shooter's ears, which also increases perceived recoil.

 

The powder burn characteristics will also impact how a gun feels on the shoulder. Two identical guns can fire identical projectiles at the same muzzle velocity, but if the powders burn differently with different accelerations in the barrel, the perceived recoil will be different.

[J-BAR #18287]

You are correct, 3rd law not 1st.

 

Apologies.

 

But I think the rest is valid.

 

Physics describes HOW matter and energy behave, not WHY they behave as they do.

[Red Logan #12252]

For every action, there is an equal or opsat reaction

[Old Scatterbrain]

You are correct, 3rd law not 1st.

 

Apologies.

 

But I think the rest is valid.

 

Physics describes HOW matter and energy behave, not WHY they behave as they do.

no need to apologize; I wasn't trying to play gotcha. I am simply trying to wrap my head around the fact that momentum is so much more important than energy in this situation.

 

This is especially frustrating to me because there was a time when this would have been so ridiculously obvious to me, and I would have been pulling my hair out trying to explain it to someone else. I do know from past experience that a few days from now I may suddenly facepalm and think "OOOOOooooohhh, now I- well geeze that was stupid!"

[Yellowhouse Sam # 25171]

The 7mm and the .375 are both custom stocked.

 

Forty hit the nail on the head. We can talk physics, momentum, energy, PF, and everything scientific until the cows come home. Those are not the big issue that matters in perceived recoil.

 

A properly fitted stock will spread the recoil evenly over the shooter's shoulder and bone structure. That eliminates pressure points which cause pain to the shooter. Pain increases his/her perceived recoil.

 

A loud muzzle blast will hurt the shooter's ears, which also increases perceived recoil.

 

The powder burn characteristics will also impact how a gun feels on the shoulder. Two identical guns can fire identical projectiles at the same muzzle velocity, but if the powders burn differently with different accelerations in the barrel, the perceived recoil will be different.

 

+1! I'll reemphasize stock/buttplate configuration. For example, a light weight 45-70 with a crescent buttplate and heavy bullets might make you cringe. The same rifle with a shotgun buttplate is often bearable in comparison.

[Forty Rod SASS 3935]

The hardest "recoiling

handgun I ever shot was a .30 carbine chambered Ruger Blackhawk that had been shortened to 4 1/5 inches and MagnaPorted. It belonged to a Gunny I worked with and he wanted to sell it. I tried it out and found out it kicked like hell.....only it really didn't. The re-directed muzzle blast from the short barrel and the carbine round (being exceptionally noisy anyway) had me flinching so bad it felt like excessive recoil.

 

I passed on buying the gun.

[J-BAR #18287]

Certainly variations in stock angle, shape, barrel length, porting, etc., from one gun to another will affect the shooter'perception or reaction to recoil.

 

But the original post was not about those variables. The original question was about two different loads presumably fired from the same gun. The two loads have differing bullet kinetic energies but produce the same momentum. If the momentum is the same then the recoil they produce will be the same.

 

And I would have passed on buying that one, too!