Interesting Caliber Momentum Comparison

[LookAtYou]

I was just thinking, isn't it weird that when comparing .556 and .45 ACP, even though the a 16" .556 has over 3x the power of a 5" .45 ACP (1174 vs 378 Ft/Lbs energy), that the .45 actually has more momentum. Not that that does or doesn't count for anything, but if comparing a 55 Gr .556 and 230 Gr .45 ACP round, respectively travelling at 3101 and 864 FPS, the .556 has a momentum of 3.3 kg x m/s (or 24.3568 Ft/Lbs) while the .45 ACP has 3.92 kg x m/s (or 28.3722 Ft/Lbs).

.556 Ammo is 55 Gr Federal XM-193 and .45 ACP ammo is Speer Gold Dot 230 Gr.

 

[Demi-human]

I was keeping along until the end...
What unit will your answer be in?
Oh, be fun and use Planck level numbers! I like lots of zeros, even if they’re infinitesimally small.

Yup, for a given speed a heavier object will have more momentum.
And, in this case, be quieter and have less range.



Now if the load was just twenty more grains, just about what I shoot from my target rifle, 75 grains at 3000fps, the venerable 45 Auto loses out, while the rifle can put the same rate of work done, out to six hundred yards.

Fun thinking!

 

[mavracer]

That's the reason that energy shouldn't be the end all answer.
That's also the reason the 5.56 won't penetrate as much sheet rock or knock over steel as rounds with more momentum.

 

[Demi-human]

Everything else being equal, and they almost never are, a bigger bullet is a better one.

 

[redneck2]

verything else being equal, and they almost never are, a bigger bullet is a better one.

Dunno about that. A 5.56 is definitely more destructive in terms of defensive situations. Speed kills.

It’s been fifty years since I took physics, but IIRC, energy is calculated by velocity squared.

I understand energy isn’t be all, end all. But, it’s the energy dump is what damages the target. Shoot a steel target at 50 yards with a pipsqueak .5.56 and a 230 grain .45 ACP.. The 5.56 will usually burn right through

 

[mcb]

And yet that 556 rd will hole 3/8 mild steel plate with ease even using a lead-core FMJ bullets and the 45 ACP won't even dent the same piece of mild steel. Kinetic energy is the only energy the bullet has to do any work (elastic or plastic deformation, material damage, noise, heat, etc ) at the target.

BUT Kinetic Energy and Momentum are inseparable quantities. If you know any two values of mass, velocity, kinetics energy, momentum the other two are also known. The idea of just looking at just Kinetic Energy or just looking at Momentum is silly the two physical quantities are inseparable and there is nothing you can do to change one without changing the other.

If you know mass, velocity, mechanical shape, and materials properties of that shape you then have a complete picture of that projectile and it's potential terminal effects. Enough so that you can do very accurate computer simulations of the terminal impact. Assuming you have equally good data on the target.

There is no need or advantage to looking at just one "number" when considering a projectile and it's terminal effects. Look at everything you can.

 

[jmr40]

Everything else being equal, and they almost never are, a bigger bullet is a better one.

Everything else being equal the bullet that penetrates deeper is the better one. And a larger caliber has to work harder to penetrate.

Momentum is a good predictor of how well a bullet will knock down a steel plate or move inanimate objects. But it means very little when predicting how well a bullet will perform in living flesh.

Both 223 and 45 penetrate enough, but velocity and energy will have an effect on how fast a living subject reacts to being hit. A hit in the vitals with either will result in the same end result, but a person hit with the 223 will go down faster.

 

[bassjam]

Dunno about that. A 5.56 is definitely more destructive in terms of defensive situations. Speed kills.

It’s been fifty years since I took physics, but IIRC, energy is calculated by velocity squared.

I understand energy isn’t be all, end all. But, it’s the energy dump is what damages the target. Shoot a steel target at 50 yards with a pipsqueak .5.56 and a 230 grain .45 ACP.. The 5.56 will usually burn right through

Well if the 5.56 is going faster, then all else isn't equal, is it?

 

[Bfh_auto]

Dunno about that. A 5.56 is definitely more destructive in terms of defensive situations. Speed kills.

It’s been fifty years since I took physics, but IIRC, energy is calculated by velocity squared.

I understand energy isn’t be all, end all. But, it’s the energy dump is what damages the target. Shoot a steel target at 50 yards with a pipsqueak .5.56 and a 230 grain .45 ACP.. The 5.56 will usually burn right through

All else being equal means the velocity would be the same.
That's where the caviot comes in. He said which they usually aren't.

 

[Riomouse911]

To be on equal velocity footing we need to get 3,100 fps...from a 230 gr .45 caliber bullet... out of a handgun...has BFR started cataloguing a .458 Win Mag revolver?

Stay safe.

 

[brewer12345]

Deer don't (usually) have steel plates on them, so the effects of projectiles doesn't really interest me. What I do care about is what it takes to put my quarry on the ground with efficiency. The size of the hole and sufficient penetration seem to me to be the primary variables. The deer I have shot with a patched round ball, cast 30 cal bullet, and jacketed 30 cal partition all seem to have died about as quickly and easily despite the very different characteristics of those things.

 

[Crosshair]

Dunno about that. A 5.56 is definitely more destructive in terms of defensive situations. Speed kills

Only because you are smuggling fragmentation into the equation.

Speed doesn't kill. Fragmentation does. Which can happen at a wide range of velocities depending on bullet type and construction.

 

[Archie]

Dunno about that. A 5.56 is definitely more destructive in terms of defensive situations. Speed kills.

Especially when driving drunk or just without attention. Not so much when hunting or defending one's life.

It’s been fifty years since I took physics, but IIRC, energy is calculated by velocity squared.

You are correct, but only if one is discussing KINETIC energy. You don't seem to remember Momentum as a form of work performed.

I understand energy isn’t be all, end all.

In this context, kinetic energy is mainly used to sell the idea of new cartridges.

But, it’s the energy dump is what damages the target. Shoot a steel target at 50 yards with a pipsqueak .5.56 and a 230 grain .45 ACP.. The 5.56 will usually burn right through

I'll remember that should I be tasked with penetrating a steel (hard surface) target. However, when the problem is to deeply penetrate a thick homologous mass, a deer, elk, cape buffalo or human attacker, momentum is preferred.

"Do you know what the gooey stuff between elephant's toes is? People who shoot them with 5.56mm rifles."

 

[mcb]

One other thing to contemplate in this. The target always has less momentum to deal with stopping the bullet than the shooter does launching the bullet. Conversely the target always must deal with significantly more kinetic energy stopping the bullet than the shooter had to deal with launching the bullet.

 

[CDW4ME]

That's also the reason the 5.56 won't penetrate as much sheet rock or knock over steel as rounds with more momentum.

Dunno about that. A 5.56 is definitely more destructive in terms of defensive situations. Speed kills.
I understand energy isn’t be all, end all. But, it’s the energy dump is what damages the target. Shoot a steel target at 50 yards with a pipsqueak .5.56 and a 230 grain .45 ACP.. The 5.56 will usually burn right through

And yet that 556 rd will hole 3/8 mild steel plate with ease even using a lead-core FMJ bullets and the 45 ACP won't even dent the same piece of mild steel. Kinetic energy is the only energy the bullet has to do any work (elastic or plastic deformation, material damage, noise, heat, etc ) at the target.

Since it was mentioned, here is a link to Winchester ammo testing, which includes 45 and .223/5.56 through steel, sheet rock, glass
https://winchesterle.com/-/media/Pr...gun-Bullet-Barrier-Testing-Protocol_2016.ashx

 

[hso]

isn't it weird

Since energy is a square function of velocity and momentum is just a direct function of velocity you shouldn't be too surprised that a relatively small mass at a higher velocity would have more energy than a much heavier one at a significantly lower velocity while momentum is going to be much more proportion to the direct function of mass and velocity. Consider the masses are about a factor of 4x apart and the velocities are 3101/864 or 3.5-ish. You square the velocity in energy to get 12-13x the energy for the same mass at the higher velocity. But your 55 gr projectile is a quarter of the 230 gr .45 reducing things to 3 times the energy of he heavier/slower bullet. Looking at the momentum, the masses are a quarter for the lighter bullet, but the velocities are only a factor of 3 more. Not enough to offset the mass difference. It is simple algebra.

 

[LiberalVet]

To be on equal velocity footing we need to get 3,100 fps...from a 230 gr .45 caliber bullet... out of a handgun...has BFR started cataloguing a .458 Win Mag revolver?

Stay safe.

You, Sir, are a menace.

But I was thinking pretty much the same thing.