Driving down steel with authority

[Ssanders224]

You guys would be hinting at what's called "impulse", measured in newton-seconds.

[Justsomeguy]

If you shoot at a "dueling tree" with various calibers you will certainly notice a difference in the authority with which heavier bullets move the limbs. Granted, a 40 loaded to major will certainly have more "momentum" than a fast moving 115grn 9mm that does not make major, but I agree that "dwell time" or the amount of time a particular type of bullet in whatever caliber can stay on the steel, will have more profound effects. A heavier bullet, having more mass, may by its very nature give more dwell time. If it's all about momentum over time, then a heavier bullet moving more slowly will have a better chance of delivering more of its total energy to the solid target.

[fltbed]

A pendulum test might be a better way to measure the energy transfered to the target, the movement of the pendulum is directly proportional to the energy transfered. The problem is the repeatability of the strike point. (All bullets must hit the same point to be valid as any difference in impact point will affect the swing.) Could send it over a chrono at the same time to verify velocity.

That’s exactly what we did many moons ago.

The contraption was call the ballistic pendulum and was used at major matches to determine “major”.

The whole thing was proven irrelevant when someone showed up with pewter bullets and literally flipped the pendulum.

It was about that time that affordable chronographs started to become available and the board came up with the mathematical Power Factor number system we use today. Still not perfect but better than what we had.

Do like most of us have. Load up different bullets, from light to heavy, to the same power factor. Take them out to the range and shoot some steel popper’s and determine for yourself what’s better.

Jeff

[njl]

A pendulum test might be a better way to measure the energy transfered to the target, the movement of the pendulum is directly proportional to the energy transfered. The problem is the repeatability of the strike point. (All bullets must hit the same point to be valid as any difference in impact point will affect the swing.) Could send it over a chrono at the same time to verify velocity.

Conservation of momentum. The momentum (M*V) is more of a factor here than the kinetic energy (1/2 M*V*V) of the bullet, because as mentioned, faster bullets tend to waste more of their energy on deformation. Ever seen highspeed film of rifle bullets hitting steel? If they don't punch right through, they pretty much explode on impact.

As for the pendulum test, never shot a spinner (the type you have to hit multiple times to get a full revolution) with varying handgun loads? Keeping the energy similar, the higher momentum ones will spin it better. Same goes for bowling pin shooting. There's a reason 9mm isn't popular where pins are shot off deep tables.

[GuildSF4]

My point was that doing a precision test with high speed camera and chrono on a pendulum, using loads at the same power factor heavy bullet Vs light bullet (Use the same caliber for both power factors) it would be interesting to see the difference in pendulum movement and bullet fragmentation. Not really the same thing as the old ballistic pendulum, just an interesting experiment. Unfortunately I do not have the camera or pendulum to perform this test.

Edited to add same bullet design for each weight, (could try different bullet constructions also).

Edited September 25, 2013 by GuildSF4

[johnsons1480]

A pendulum test might be a better way to measure the energy transfered to the target, the movement of the pendulum is directly proportional to the energy transfered. The problem is the repeatability of the strike point. (All bullets must hit the same point to be valid as any difference in impact point will affect the swing.) Could send it over a chrono at the same time to verify velocity.

Conservation of momentum. The momentum (M*V) is more of a factor here than the kinetic energy (1/2 M*V*V) of the bullet, because as mentioned, faster bullets tend to waste more of their energy on deformation. Ever seen highspeed film of rifle bullets hitting steel? If they don't punch right through, they pretty much explode on impact.

As for the pendulum test, never shot a spinner (the type you have to hit multiple times to get a full revolution) with varying handgun loads? Keeping the energy similar, the higher momentum ones will spin it better. Same goes for bowling pin shooting. There's a reason 9mm isn't popular where pins are shot off deep tables.

If your formula for momentum is Mass x Velocity, then you have reduced this to power factor.

Mass x Velocity

115 gr x 1173.91 fps = 135,000

124 gr x 1088.71 fps = 135,000

147 gr x 918.367 fps = 135,000

So, by your example, the momentum is the same for each selected bullet weight loaded to the same power factor.

[GuildSF4]

Yes momentum is the same, impulse is not. The OP's question was do heavier bullets work better at the same power factor. So it would be nice to have a test to prove it or not.

[Flexmoney]

Lets take a look here...

Newton's 3rd.

(mass x velocity of the bullet) plus the (Mass x Velocity of the target) need to equal zero

mb * vb + Mt * Vt = 0, or...

mb * vb = Mt * Vt

We can know the mass of the bullet and it's velocity, plus we can know the mass of the target. We are looking to solve for the Velocity of the target.

Since we are talking about a fixed target mass, the velocity of the target would be the same in all circumstances where the power factor was the same...regardless of bullet weight. However...

We have observed that that is not the case. Our observation are that heavier bullets (given the same power factor) tend to move steel better. Why?

- Conservation of Momentum tells us that the steel should move the same, given the same power factor, regardless of bullet weight.

- We should also maintain Conservation of Momentum whether the collision is elastic or inelastic (inelastic meaning a loss of kinetic energy). Therefore, the bullet falling apart, in itself, shouldn't change the momentum, right? However... a smaller bullet would tend to fall apart more quickly that a more massive bullet?

- Also, a well constructed bullet would tend to stay together longer.

- For that matter, given the same diameter (caliber) a heavier bullet would be longer in length, and that length would give it more time to act on the target.

- Given the same power factor, a heavier bullet will also be moving slower...which should give it more "push" time on target, I'd think.

- - - Impulse, is the average force applied over time....a change in linear momentum of an object. The longer the force acts on the target, the greater the increase in acceleration and velocity.

?

[Mbauer67]

When trying to analyze this type of dynamic system one must understand the variable known as "e". E is a variable with a value from 0-1, essentially it is the engery lost during an impact between 2 objects. Unless you are shooting in an airless vaccum you will always lose a certain amount of energy during an impact. If very little energy is lost, then the closer e will be to 1.

It is almost impossible to predict the value of e but you can get fairly close with educated assumptions, if I had to guess I would say the slower moving heavy bullets have a higher e value thus making them transfer energy more efficiently to the target.

Of course e becomes zero if you miss the target, and will decrease rapidly as the angle between the approaching bullet and the target moves away from 90deg.

So in simple words, don't miss, and work on your shot timing first. Then you won't be so worried about the power factor

[IDescribe]

Given similar momentum, a slower bullet spends more time on target because it takes longer to compress to its limit before it fights back and the energy takes the bullet elsewhere. Momentum is built over time, so a slower bullet that spends more time on the target builds more momentum in the target. That apparently outweighs the energy advantage for the lighter, faster bullet. (NOTE: this is a guess, not some confirmed wisdom or knowledge.)

Or someone could just take some 115 grain 9mm and 147 grain 9mm, build them to the same power factor, and see if the 147 grainer can consistently knock over a particular popper with lower shot placement than the 115.

Edited September 28, 2013 by IDescribe

[TonyT]

I believe the better measure of steel knockdown capability is momentum which is MV vs energy which is MVsquared. In any case the heavier bullets seem to do better in my loads.

[Akkid17]

I think that experiment would be great especially if you get all the bullets for the different weights from the same manufacturer and hopefully the materials from the same lots to make it as consistent as possible across the weight range. Bayou makes 9mm and 38 special bullets from 105 up to 160gr. I may have to get some sample packs from him to do a little experimenting since I'm already placing an order.

[warpspeed]

So in simple words, don't miss,

I knew I was doing something wrong.

[IDescribe]

So in simple words, don't miss,

I knew I was doing something wrong.

Oh well, sure, if you want to go with good shooting, then it's easy.

[Alaskapopo]

I've heard it over and over again that the reason people like to use heavier bullets in 9mm is because they, "drive down steel with authority." Can someone help explain that to me? Using the BC from Hornady's FMJ (so I would have as direct a comparison as I could think of), I came up with the following chart. This is assuming that each bullet is loaded to 135 PF.

ETA: The editor didn't like my html table, so here's a picture

Energy is not what drives down steel its momentum. Momentum is the amount of force it takes to bring a moving object to rest. (ie power factor) A 165 grain power factor load rather it be one with 500 foot pounds or just 200 will bring steel down the same.

[Miranda]

first answer is: hit center and all are the same.

second answer is: what happens when you don't quite get the center?

the steel flexes...

does the target bind in any way that requires more energy to fall?

I have no doubt that a deflected bullet will not transfer
all the potential energy.
I am also sure a heavier bullet will transfer more energy in a deflection.

the energy in the mass of the bullet is what transfers in a deflection.

miranda