Driving down steel with authority

[johnsons1480]

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

Edited September 23, 2013 by johnsons1480

[razorfish]

I've heard the same thing, but the science doesn't seem to support this.

If the Kinetic Energy of the bullet hitting the target is the reason the target falls then velocity has more effect than mass.

where m = mass of object (bullet weight)

v = speed of object (speed/FPS)

Notice that because velocity is squared in the above formula for Kinetic Energy it has more affect than Mass (bullet weight) on the amount of Kinetic Energy created.

Again, I'm not saying Kinetic Energy is the only force at work, but simply the only one I can think of.

I'm currently facing the dreaded MGM spinner, so I would love the answer to this question... Heavier or Lighter bullet?

[Matt Cheely]

It's all about where the energy goes when it hits the popper.

A slow moving bullet will impart all its energy into knocking over the popper, and generally bounce off in one piece. Think of all the lightly loaded 45 rounds that bounce off and land in the range next door.

A fast moving bullet will take a large piece of the energy and use it to rip the bullet apart. Think of how much it would take to pull a bullet into so many little pieces of lead.

That fast bullet might have more energy, but it doesn't put it all into the popper.

[razorfish]

A slow moving bullet will impart all its energy into knocking over the popper, and generally bounce off in one piece. Think of all the lightly loaded 45 rounds that bounce off and land in the range next door.

A fast moving bullet will take a large piece of the energy and use it to rip the bullet apart. Think of how much it would take to pull a bullet into so many little pieces of lead.

That fast bullet might have more energy, but it doesn't put it all into the popper.

Thanks... It looks like some heavier bullets are in my immediate future.

[Flexmoney]

I have a reloading manual (Sierra) that refers to "dwell time" when speaking of their bullets, made for shooting steel silhouette targets.

Like Matt, I agree with the idea of transferring the energy to/into the target.

[johnsons1480]

I have a reloading manual (Sierra) that refers to "dwell time" when speaking of their bullets, made for shooting steel silhouette targets.

Like Matt, I agree with the idea of transferring the energy to/into the target.

You reminded me of something, and I thought we were on to something there in the way of explaining this, "scientifically." Taylor's KO Factor is a method of better judging hunting calibers knock down or knock out factor. His theory is that energy is not the deciding factor of knock down (like you all are stating). Very similar to what we're looking at. So I ran the numbers and .... Not much. It shows me that these are pretty evenly matched. Here is the method and the numbers

(Equation 1)

Where

• is the bullet mass in grains (1 pound = 7000 grains)
• is the bullet velocity in feet per second
• is the bullet diameter in inches

Please understand that I mean no disrespect. I know that all of you have much more practical application of this than I do. I'm just trying to get some numbers to support the theory.

[Matt Cheely]

All the "scientific" formulas you will pull out will not matter as they won't take into account the loss of energy in the bullet ripping apart. The kinetic energy equation only works if there is no energy loss, including friction & etc.. Same for a ballistic knock down equation, that assumes all the energy is going into the "target/animal".

If you really wanted to figure it out, you could setup a target on a "frictionless" surface and measure the acceleration & velocity at which it moves just after being shot with a high speed camera. Compare the actual energy transferred to that target, vs the theoretical kinetic energy that should have been in the bullet and you'll see how much you lost in the transfer.

[GuildSF4]

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.

[JAFO]

I have a reloading manual (Sierra) that refers to "dwell time" when speaking of their bullets, made for shooting steel silhouette targets.

Like Matt, I agree with the idea of transferring the energy to/into the target.

You reminded me of something, and I thought we were on to something there in the way of explaining this, "scientifically." Taylor's KO Factor is a method of better judging hunting calibers knock down or knock out factor. His theory is that energy is not the deciding factor of knock down (like you all are stating). Very similar to what we're looking at. So I ran the numbers and .... Not much. It shows me that these are pretty evenly matched. Here is the method and the numbers

(Equation 1)

Where

• is the bullet mass in grains (1 pound = 7000 grains)
• is the bullet velocity in feet per second
• is the bullet diameter in inches

Please understand that I mean no disrespect. I know that all of you have much more practical application of this than I do. I'm just trying to get some numbers to support the theory.

Unfortunately, that TKOF looks more suitable for comparing different calibers. Since d is a constant in your comparison, you've reduced the formula to the same as power factor = (m)(v)

[johnsons1480]

I have a reloading manual (Sierra) that refers to "dwell time" when speaking of their bullets, made for shooting steel silhouette targets.

Like Matt, I agree with the idea of transferring the energy to/into the target.

You reminded me of something, and I thought we were on to something there in the way of explaining this, "scientifically." Taylor's KO Factor is a method of better judging hunting calibers knock down or knock out factor. His theory is that energy is not the deciding factor of knock down (like you all are stating). Very similar to what we're looking at. So I ran the numbers and .... Not much. It shows me that these are pretty evenly matched. Here is the method and the numbers

(Equation 1)

Where

• is the bullet mass in grains (1 pound = 7000 grains)
• is the bullet velocity in feet per second
• is the bullet diameter in inches

Please understand that I mean no disrespect. I know that all of you have much more practical application of this than I do. I'm just trying to get some numbers to support the theory.

Unfortunately, that TKOF looks more suitable for comparing different calibers. Since d is a constant in your comparison, you've reduced the formula to the same as power factor = (m)(v)

That's a valid point; I had not considered that. If I had not rounded the velocity numbers from the power factor calculation, the TKOF numbers would have been identical. Thanks for pointing that out!

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.

I like this idea. Has no one ever done this? I don't have the equipment to do this kind of experiment, but I would like to see it done.

[cecil]

i guess it depends on how hard you want to knock the steel targets down... i shoot 9mm 124 gr with a power factor of 135... if the target is set properly and you hit it in the center mass.. it will fall..

[Sarge]

Well, my 9MAJOR 121's knock down steel far better than any of my minor 147 loads ever did. At some point velocity must trump mass, no?

And what about different bullet designs? Certainly some bullets disintegrate more or less than others of the same weight.

[RDA]

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.

I just happened to see this, at the end of the video, they compare the knockdown power of 223 50 gr. and 300BLK 125 gr. In slow motion, you can see that both hits are similar distances from the axis so I believe it is a reasonably accurate comparison, similar to the pendelum test you are recommending.

Edited September 23, 2013 by RDA

[johnsons1480]

Well, my 9MAJOR 121's knock down steel far better than any of my minor 147 loads ever did. At some point velocity must trump mass, no?

And what about different bullet designs? Certainly some bullets disintegrate more or less than others of the same weight.

That's a very good point. I meant to ask this earlier, but how is a bullets disintegration not equal to it dumping its energy into the target? The front connects, the tail end keeps going. The front either mushrooms or fragments, but the energy is still imparted into the steel. The steel isn't like an animal where the energy may be transferred out the other side. AR500 steel completely absorbs the bullet impact. Here's an example of that.

The bullet smashes completely into the target. There isn't any more energy to be imparted. Maybe I'm just not seeing this correctly?

[johnsons1480]

Unfortunately, that TKOF looks more suitable for comparing different calibers. Since d is a constant in your comparison, you've reduced the formula to the same as power factor = (m)(v)

I thought about this some more. If we were loading ammo to the same power factor, then the number should be the same. But if you were to take ammo loaded to it's full potential in a given caliber, you would get more relevant data. For instance, a 308 in 150 and 165 grain Nosler Accubond.

What I'm getting at is, since we load these bullets to nearly the same power factor on purpose, we will get nearly the same KO Factor. As Sarge stated, 121 bullets loaded to major will "knock down steel far better than any of my minor 147 loads ever did." Maybe the power factor is a decent indication of the knockdown after all.

[Ssanders224]

Well, my 9MAJOR 121's knock down steel far better than any of my minor 147 loads ever did. At some point velocity must trump mass, no?

And what about different bullet designs? Certainly some bullets disintegrate more or less than others of the same weight.

That's a very good point. I meant to ask this earlier, but how is a bullets disintegration not equal to it dumping its energy into the target? The front connects, the tail end keeps going. The front either mushrooms or fragments, but the energy is still imparted into the steel. The steel isn't like an animal where the energy may be transferred out the other side. AR500 steel completely absorbs the bullet impact. Here's an example of that.

The bullet smashes completely into the target. There isn't any more energy to be imparted. Maybe I'm just not seeing this correctly?

"There isn't any more energy to be imparted"

Yes there is. If and piece of the bullet leaves the steel, or fragments, that is energy leaving as well.

Like Cheely has already said, when a bullet contacts a steel plate, energy is dissipated several different ways.

[mpeltier]

Well, my 9MAJOR 121's knock down steel far better than any of my minor 147 loads ever did. At some point velocity must trump mass, no?

And what about different bullet designs? Certainly some bullets disintegrate more or less than others of the same weight.

I think your correct on both counts. Your second point fits in with what matt is saying to a point as well.

I really think shot placement is more important (to 9mm minor, as in the op's examples) than anything else. My experiance has been most complaints of knocking down steel is coupled with an edge or low shot and its easier to blame the ammo than yourself.

[Steve RA]

It's the momentum of the heavier bullet that helps knock the steel over. IHMSA shooters go through this all the time.

[Ssanders224]

It's the momentum of the heavier bullet that helps knock the steel over. IHMSA shooters go through this all the time.

Not quite.

p=mv

What we call "power factor" is just momentum.

All the projectiles (if loaded to equivelant PFs) will have basically the same "momentum".

[johnsons1480]

It's the momentum of the heavier bullet that helps knock the steel over. IHMSA shooters go through this all the time.

Not quite.

p=mv

What we call "power factor" is just momentum.

All the projectiles (if loaded to equivelant PFs) will have basically the same "momentum".

See that makes sense to me. I don't see any science or anything but anecdotal evidence to back up what is being said here about heavier bullets. If it can be shown to me, I would be happy to believe it without an argument. I just see no evidence to back up heavier bullets driving down steel better.

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[JAFO]

That's a very good point. I meant to ask this earlier, but how is a bullets disintegration not equal to it dumping its energy into the target? The front connects, the tail end keeps going. The front either mushrooms or fragments, but the energy is still imparted into the steel. The steel isn't like an animal where the energy may be transferred out the other side. AR500 steel completely absorbs the bullet impact.

A bullet entering ballistic gel/an animal/etc that does not come out on the other side has expended all of it's energy in the target. One that bounces off hasn't. All those pieces that go flying off to the sides and imbed themselves in the nearest object still contain energy.

Personally, I've never had a problem knocking steel down with 124s, either. I'm trying 147s because of the different recoil feel.

[razorfish]

Could it have something to with the idea that a heavier bullet moving slower transfers it's energy more slowly and/or over a longer period of time than a faster but lighter bullet?

It doesn't take much force to push a popper over... I can do it with a single finger. I imagine that I can push down the popper with little force because my finger accelerates the heavy steel slowly and therefore I don't waste a lot of energy trying to accelerate the steel, but instead I use just enough effort to start it moving and then apply a bit more force to push it over.

So basically is a slower but heavier (ie. bigger) bullet spending more time on the steel, therefore it has more time on target to begin to accelerate the steel target?

Edited September 24, 2013 by razorfish

[Flexmoney]

FYI: http://www.sierrabullets.com/resources/bullet-selection/

Full Profile Jacket (FPJ) is a design concept featuring a thick, tough jacket that covers the entire profile of the bullet. Intended for maximum momentum transfer to steel targets, this design generates good dwell time on the target for maximum "push."

[warpspeed]

It doesn't take much force to push a popper over... I can do it with a single finger. I imagine that I can push down the popper with little force because my finger accelerates the heavy steel slowly and therefore I don't waste a lot of energy trying to accelerate the steel, but instead I use just enough effort to start it moving and then apply a bit more force to push it over.

I think you are not taking into account just how much mass is at work. Hint: it is not just your finger.

[razorfish]

I think you are not taking into account just how much mass is at work. Hint: it is not just your finger.

I still suggest that it takes very little force. Imagine walking behind the popper and hooking a trigger pull gauge to the popper. Now gently and slowly pull. I bet it barely measure the amount of force to "slowly" pull the popper to the point it falls down. Small amount of force but an extended time period.

I think Kyle nailed it right away when he said "Dwell Time". I totally missed it until he added the quote from the Sierra website.