Physics Guys

[mwc]

Using two different Brinnell hardness of boolits, say one at a B11 and another at a B18, both at the same weight, and the same muzzle velocity, how much of the energy is redirected or lost when hitting a steel target?

[44MAG#1]

Are you actually asking which bullet will have more "hang time" on the plate before going,to pieces? Or, are you asking something different?
i've shot plates with both hard and soft and really see no difference that can be measured with the eye. The energy lasts only a Micro second with both regardless. The energy lasts from first contact until the bullet disintegrates and that is where energy stops or momentum too.
if the bullet hits the plate at 1100 fps and it doesn't penetrate and it stops as soon as the base is consumed by being turned into exploding dust how long does that take? I would figure may be .0000758 seconds on a bullet one inch in length thereabouts. Probably a little longer due to the velocity ramping down as the bullet is consumed.
So why does this matter?

[mwc]

I'm having issues with a swing plate, trying to get it to make a complete revolution, I'm using pc'd boolits that are usually fine for everything else, my B11 coated won't seem to move the swinger as much as a harder plated round of the same weight, also some "factory" hard cast that are B18 seem to move it better, I know a lot of this has to do with my abilitys or lack of them, just trying make my cast work.

[44MAG#1]

What caliber, bullet weight and velocity and the weight of the pendulum?
And why the complete,Revolution? Just for the wow factor?

[mwc]

I'm using a 38 special S&W MDL 627, shooting 158 gr, MV is 820, making a power factor of 129.5, the complete sping is what is required of that particular stage set up, or take a large time penalty. Using the same alloy, I can spin it with my 625 45acp with 230 gr, MV of 750 which is greater power factor, but I can use a harder alloy that I have mixed, and use a 130 gr. Mv 1000 fps in my 986 9mm with a power factor 130, and spin it. Comparing the 38 and the 9 the power factor is pretty close, the only difference is alloy hardness.

[rsrocket1]

You need to test the bullet that fails (158g 38SP soft lead @ 820 fps) and compare it to what you think "ought" to work (158g 38SP plated @ 820 fps). Compare apples to apples. Or up the charge on the 38 special loads to see how much more pf you need to swing the plate over. It might or might not be a big deal in terms of added recoil for you.

...from a Physics guy

[44MAG#1]

Have you tried the same alloy in the 38 that you use in the 9MM? If not why? What kind of game is this?

[mwc]

Acually the 158 gr soft lead @820 won't spin the target but a 158 jacketed at 820 will, the jacketed seems to hold together longer to drive the target more than just blowing up like when the soft lead does. I haven't tried the same alloy used in the 9 in the 38 because I guess I'm just cheap and not wanting to use more tin and antimony, when I blended that mix I was pushing the 9 a lot faster and hotter, but for 90% of the rest of the time the soft mix works great. This is a Falling steel challenge game, we shoot it every Tues. night, usually 4-5 stages with the round count any where from 15 to 32 per stage, different scenarios every week, all done in the shortest time wins. Nothing important, but a lot of fun.

[rsrocket1]

Did you figure out how much more powder you needed in the lead 38 special bullets to make it work?

Don't get hung up on the PF numbers. You might find out that an extra 0.3g gives you enough pop to swing the target and you may not even notice (you'll have to do a "blind test" otherwise you may get jaded).

0.3g per cartridge is about 1/10th of a penny per shot even at inflated $30/# powder prices.

[seaboltm]

sounds like a f delta t = m delta v issue. The issue of making a target spin is the transfer of momentum, not energy, per se. delta t is the amount of time the force f is applied. delta v is how much the velocity will change due to the applied force for the amount of time (delta t). So, if a bullet stays together longer the delta t will be longer, hence the delta v will be longer, meaning more momentum is transferred, hence more "spin" on your target.

With your initial conditions of same mass same velocity, we will assume the force f is the same. There are other factors, but lets ignore those and just concentrate on your question, spinning the target. Both B11 and B18 bullets are in contact with the target for a short period of time, but even 10% more time before disintegrating means 10% more momentum transferred to the target. That's significant.

[fouronesix]

sounds like a f delta t = m delta v issue. The issue of making a target spin is the transfer of momentum, not energy, per se. delta t is the amount of time the force f is applied. delta v is how much the velocity will change due to the applied force for the amount of time (delta t). So, if a bullet stays together longer the delta t will be longer, hence the delta v will be longer, meaning more momentum is transferred, hence more "spin" on your target.

With your initial conditions of same mass same velocity, we will assume the force f is the same. There are other factors, but lets ignore those and just concentrate on your question, spinning the target. Both B11 and B18 bullets are in contact with the target for a short period of time, but even 10% more time before disintegrating means 10% more momentum transferred to the target. That's significant.

^^ That's it in a nutshell. Well said

[MBTcustom]

sounds like a f delta t = m delta v issue. The issue of making a target spin is the transfer of momentum, not energy, per se. delta t is the amount of time the force f is applied. delta v is how much the velocity will change due to the applied force for the amount of time (delta t). So, if a bullet stays together longer the delta t will be longer, hence the delta v will be longer, meaning more momentum is transferred, hence more "spin" on your target.

With your initial conditions of same mass same velocity, we will assume the force f is the same. There are other factors, but lets ignore those and just concentrate on your question, spinning the target. Both B11 and B18 bullets are in contact with the target for a short period of time, but even 10% more time before disintegrating means 10% more momentum transferred to the target. That's significant.

Bingo. Perfect explanation IMHO.
Of course, on a soft/thick target like a deer, the object is to affect as much of the tissue as possible as well, but in that case, a hard bullet will pencil right on through, where a soft bullet will "follow the shock wave" as it expands, delivering more energy as it goes.
You have to match the bullet to the application. Hard for hard, soft for soft, and tough for tough etc etc etc.

[mwc]

Thank You guys for the responses,seboltm, I thought that was the results that I have been seeing but couldn't quite put it in words, and wasn't sure if I'm just imagining it or rationalizing my bad shooting.

[seaboltm]

Thank You guys for the responses,seboltm, I thought that was the results that I have been seeing but couldn't quite put it in words, and wasn't sure if I'm just imagining it or rationalizing my bad shooting.

No sweat. After 12 years of studying physics to the phd level, I would like to think I can explain it.

[kens]

the simple answer is .45-70.
that'll swing it!!!:kidding:

[Hickory]

the simple answer is .45-70.
that'll swing it!!!:kidding:

Yes, increasing the mass will do it too.

[runfiverun]

soft don't break apart as easily as hard.
that's why we soften our hunting alloy's then artificially harden it again, this works extremely well in a certain velocity window.
change the velocity window and your alloy goal [and necessary meplat diameter] changes.

now when it comes to jacketed you use a softer alloy [usually near pure] as a core for varmint bullets.
the trick there is speed and jacket manipulation.

a slower, heavier, softer boolit may be what you want.

[kens]

I have the LEE .45acp truncated cone boolit mold, for some reason it seems to thump steel better than my other molds.
why the truncated cone? it the same alloy as the others.
could it be the large meplat?

[popper]

mwc - try adding some copper via CuSO4 method on your soft alloy. Or you can use sulfur but it is messier. Definitely will let the boolit hang together longer. Both are cheap and easy.

[44MAG#1]

Actually the problem revolves around the OP's problem of cheapness. I am cheap too, so no offense meant by that, as in this day and age we need to be cheap.
The cheapness keeps him from using the same alloy as his 9MM bullets which at almost the same momentum will swing the plate the way he wants verses the alloy in his 38's that won't.
How much more in a year will he spend on the better alloy verses the lackluster alloy? 10, 15 or 20 percent?
If he spends 150 buck a year on the bullets he uses in the 38 Special DURING competition and one adds 20 percent more that is 30 bucks extra. In Practice bullets use the cheaper alloy since in practice whether the plate rotates or not is moot.
Now 30 bucks more really isn't a lot over a year. One could cut out a few snacks and gain it back and probably be healthier too.
Now if his playtime isn't important enough to make a small sacrifice it makes me wonder if it is worth doing in the first place.
Now my answer to the alloy is use the better alloy, drop some other money taking junk to make up the slight added cost and enjoy the "game" or drop it.

[garym1a2]

It depends on twist rate and RPM of the boolit. Plus the fit,

[yovinny]

I'm not a physicist, just a dumb, uneducated city boy.
But if this is a hanging target on a pivot, your dealing with a cantilever, so exactly 'where' on the plate you hit it will change the length of your lever and make quite a difference.
Do both loads hit at the same exact POI ?

[wv109323]

Could you just add counterweight to the opposite side of the pivot point and fine tune the point at which the plate makes a 360 revolution?

[fouronesix]

No sweat. After 12 years of studying physics to the phd level, I would like to think I can explain it.

:) I figured there was some background reflected in the response. Momentum is intuitive by nature while kinetic energy is not. Confusion usually surrounds the application or understanding of both concepts- especially when discussing ballistics in threads like this one.

[DrCaveman]

Try water dropping your boolits (if you aren't already) and leave everything else the same

[44man]

Boolit weight and more velocity! The heavy steel feels no more then the little .38 feels in your hand.
The .357 at IHMSA shoots would not take all the steel so they came out with the max that could shoot 200 gr bullets at near 1800 fps with a momentum of .97. The 158 in the .357 mag only had .64. The .38 is most likely in the .4 range. The .44 could be borderline with a figure of 1.03.
Hang time of a bullet on steel can apply more momentum but nothing matches weight or velocity.

[mwc]

Could you just add counterweight to the opposite side of the pivot point and fine tune the point at which the plate makes a 360 revolution?
Check out the mgmtargets web page and look at the gravity moving targets, if you click on the single spinner there is a video of what target I'm talking about.

[mwc]

Try water dropping your boolits (if you aren't already) and leave everything else the same
Where I'm PCing my boolits and baking the pc that will negate any water quenching effects.

[mwc]

mwc - try adding some copper via CuSO4 method on your soft alloy. Or you can use sulfur but it is messier. Definitely will let the boolit hang together longer. Both are cheap and easy.
I have ordered some of the 7% cu babbit from roto metals, that I will alloy into some of the alloy I have. I may try to use the CuSo4 method also, but from what I understand, the sulfate takes on the tin first then any zinc. Since I don't have zinc in my mix won't this take out the tin and replace with copper, then I would have to add some more tin back to the mix. If I just use pure lead and throw in some zinc, then sulfate to add copper then tin and some antimony. I think that your right if I make the boolit tuffer should also give the same results as will making the mix harder to achieve similar results.

[mwc]

Boolit weight and more velocity! The heavy steel feels no more then the little .38 feels in your hand.
The .357 at IHMSA shoots would not take all the steel so they came out with the max that could shoot 200 gr bullets at near 1800 fps with a momentum of .97. The 158 in the .357 mag only had .64. The .38 is most likely in the .4 range. The .44 could be borderline with a figure of 1.03.
Hang time of a bullet on steel can apply more momentum but nothing matches weight or velocity.
A lot of this whole issue is based on my ability and consistance at shooting and hitting the target at the right time, I have been able to spin the target with just 5 shots using my MD625, 45acp using 230 RN. I have been able to do the same thing with 10 shots from my 9mm using 130 RN. So far with 16 good hits I haven't been able to spin it with my 38 spcl. check the video out on mgmtargets site under gravity moving, or under skillbuilders targets. It's fun but frustrating.

[olafhardt]

The problem with applying physics to this situation is that it is not an elastic collision. Deformation of metal requires energy which is converted into heat which is why the plates warm up. The energy is conserved and so is the momentum. This can all be worked out mathematically which is complicated and will be different for each boolit. Since the harder, tougher bullets usually have more elastic collisions they should theoretically swing plates higher. This is more easily studied with a gun and boolits and a reloading manual than a calculator, pencil and physics book.

[Ballistics in Scotland]

What caliber, bullet weight and velocity and the weight of the pendulum?
And why the complete,Revolution? Just for the wow factor?

I can see what the OP is getting at. If a bullet entered a massive wooden pendulum and got stopped without disintegration, all of its energy (except for some heating of the wood fibres) would be transformed into forward momentum in the block. If the bullet disintegrates and some of the fragments are hurled sideways, some of that energy isn't transformed into forward momentum. The same would apply if you fired a hard steel ball bearing, which bounces. What the bearing still has, the pendulum doesn't.I

It seems entirely logical that different bullet hardnesses may do that to a different degree, although I suspect that the difference is negligible. You could determine it like Robins in the 18th century by using a heavy pendulum which draws a tape, nylon monofilament or cord through a loose eyelet as it moves, but doesn't feed it back though as it returns to the vertical. The bullet which pulls though the greatest length of tape has imparted the most momentum to the pendulum.

In answer to your signature, mass is a measure of how much matter is in an object, and weight is a measure of how much the earth's gravity pulls on it. If some cataclysm of nature had caused the human race to evolve exclusively on mountain tops, the kilogramme would be very slightly less. If you take a cannon-ball of the 68lb. size into space, it will hover in mid-air like a soap-bubble, because no planet attracts it, and it has no weight. Kick it and you will damage your toe as much as anywhere else, since if no iron has been removed, its mass is the same as ever.

[Taylor]

Makes me wish I had finished 3rd grade.:shock:

[44man]

Friend bought me a .22 swinger. No bullet on earth will swing it. Maybe my .44 will make it loop.

[DrCaveman]

Where I'm PCing my boolits and baking the pc that will negate any water quenching effects.

Ok, mr difficult (kidding)

Add more powder, as suggested by many. Or use your harder alloy, as suggested by many. You cant defy physical reality, and you are looking it in the face

[rsrocket1]

This isn't so much a Physics problem as it is a testing problem. If you simply worked up a load with your favorite cheap bullet to where it swings any target regardless of where you hit it, add a bit more powder to account for variations in drop as well for mushiness in your grip vs benchrest (or not), you will be able to swing a target with that load no matter where you hit it. Don't waste your time trying to theorize and experiment. That is, unless you are getting enjoyment from that too which is OK if that's what floats your boat.

[Wayne Smith]

Some of us are just plain curious. I found out 'what' but I want to know "why"!

[44man]

Want to see steel fly, use a 440 gr from a .500! It is a hoot.

[BenW]

Hardness makes no difference in how much momentum is transfferred to the plate, unless the bullet ricochets. Momentum is conserved in every direction through all events, no matter how long the event is. The only way to get the plate to move back more is for the bullet to reverse direction (ricochet). That's why your fmj ammo is enough, but the lead isn't.

[Certaindeaf]

http://ts1.mm.bing.net/th?&id=JN.Dkbna9S/%2bFRBKrEIAliJ0w&w=300&h=300&c=0&pid=1.9&rs=0&p=0

[dondiego]

E=mc2

[BenW]

Let's look at it from an Engineering perspective:

Rule 1: Momentum is conserved
Rule 2: Mass is conserved

So you have a bullet, mass of "m" is fired at "v" velocity. The plate, mass of M, is moving at V velocity.

Before impact is labeled as "1" and after impact is labeled "2".

[mass of bullet before impact] = m1
[velocity of bullet before impact] = v1
[mass of plate before impact] = M1
[velocity of plate before impact] = V1 = 0 (not moving)

[mass of bullet and its fragments after impact] = m2 = m1 (see Rule 2)
[mass of plate after impact] = M2 = M1
[velocity of bullet after impact] = v2 (unknown)
[velocity of plate after impact] = V2 (unknown)

There are 4 possible impact reactions:
1 - bullet passes through (we'll ignore this since it didn't happen in testing)
2 - bullet sticks to plate (ignore this as well, since they just combine mass and is the worst possible scenario)
3 - bullet hits plate and stops all forward motion, fragments are sent in a circle parallel to the plate
4 - bullet bounces back at almost full speed

So, the momentum of the system at all times, P, is conserved (see Rule 1).

Before impact:

P = m1 x v1 + M1 x V1 => P = m1 x v1 [since the plate is stationary]

After impact:

[if the bullet stops completely] P = m2 x v2 + M2 x V2 => P = M2 x V2 [since bullet is now not moving forward]

[if bullet bounces back] P = m2 x v2 + M2 x V2

So the velocity of the plate, V2 can either be:

V2 = P/M2

OR

V2 = [P - m2 x v2] / M2

Since v2 is negative (it reversed direction) the second scenario where the bullet ricochets moves the plate more.

Now we've found the velocity of the plate (once we plug in the numbers and choose which reaction to "test"), we can now find out if the plate makes a complete spin.

[gravitational acceleration] = g
[radius of arc of the arm] = R
[Energy of the plate] = E
[Mass of the plate] = M

Rule 3: Energy is conserved

Since the plate is no longer going to waste energy through sound or friction (such as from the impact), it'll conserve energy.

Right after impact:
E = (M x V2 x V2) / 2

If the plate barely reaches the top of its swing, with no movement left:

E = 2 x R x M x g

Why? Because energy is force times distance. You are, in a round-about way, lifting the plate from the bottom of it's arc to the top, a distance of [2 x R]. The force is its weight, or [M x g]

We combine the equations:

(M x V2 x V2) / 2 = 2 x R x M x g

V2 x V2 = 4 x R x M x g / M

V2 x V2 = 4 x R x g

V2 = squareroot(4 x R x g)

V2 = 2 x squareroot(R x g)

That is the minimum velocity from the plate required after impact to make a full swing.

Trying to calculate how long the bullet is in contact with the plate, how much it deforms, etc is complicated and only tells us how much the bullet bounces back. I cheated and gave you a range it will be in (between bullet splattering and bullet bouncing back).

******************************

Short story is, you can either increase the powder charge (more velocity and cost) or you can make your bullets ricochet. I know what choice I'd make.

-Ben

[44MAG#1]

Does anyone really care about the formulations on this?
The OP already knew the answer. He was too conservative on money to use the alloy he had success with at the same momentum.
This is a question concerning his money verses success in the area of ballistics.