Please help me understand knockdown power (on steel plates)

[igolfat8]

We are not talking about deadly knockdown power here, though it may run a parallel path? I am loading .40 S&W cartridges. If I load a 145 and 175 cast boolit and both have the same FPS velocity through a chronograph will they have equal knockdown power on steel plates? This last season I was shooting 145s and am thinking about going to a heavier boolit if that will work more efficiently on off center hits. Is there a math formula to figure this out?

[high standard 40]

I have been shooting handgun silhouette since 1980. There is a math equation to determine bullet momentum.

Take bullet weight in grains and multiply times the remaining velocity at the target, then divide by 225200.

This will provide the momentum factor for that load. The higher the number, the better. Additional velocity or bullet weigh will increase momentum.

[ipijohn]

We are not talking about deadly knockdown power here, though it may run a parallel path? I am loading .40 S&W cartridges. If I load a 145 and 175 cast boolit and both have the same FPS velocity through a chronograph will they have equal knockdown power on steel plates? This last season I was shooting 145s and am thinking about going to a heavier boolit if that will work more efficiently on off center hits. Is there a math formula to figure this out?

Yep Mx(VxV)

[fishhawk]

no. Say you take a bowling ball and move it at 500 FPS and a ping pong ball at also 500 FPS which one is going to knock pins over? Yes it's over simplified but the same thing happens with boolits.

[claude]

If I load a 145 and 175 cast boolit and both have the same FPS velocity through a chronograph will they have equal knockdown power on steel plates?

No, it takes less work to bring a 145gr bullet to 1200fps than it takes to bring a 175gr bullet to 1200fps these two bullets will necessarily have different kinetic energy, the 175 will have more energy to transfer when it hits the target, so it will hit harder. That's the short answer, if you want to get all mathematical, go here;

http://en.wikipedia.org/wiki/Kinetic_Energy

[Doc Highwall]

Here is a sit that has the information that you want.

http://www.lasc.us/ConversionTables.htm

[theperfessor]

Momentum is what moves things. A slow, heavy bullet has a longer dwell time on the target and transfers more momentum. Imagine a large, massive safe door. Punch it as hard as you want and see if you can close it. Then push on the door for a couple of seconds. See which method moves the door.

Momentum = mass * velocity

Energy = 1/2 * mass * velocity squared

Similar terms, different concepts

[bmortell]

+1 to the perfessor. if you look in the stickies section theres video of bullets on steel with high speed camera. bullets hit and peel away like a banana. therefore slow bullets push on it longer, and also push time is affected by bullet length in a linnear fashion.

[popper]

Interesting that the momentum equation uses mass-force where the energy equation uses mass-weight. Oh, that is because momentum is a vector quantity, has direction. I would just go with P.F. Yes, the heavier boolit has more energy to transfer to the steel plate, giving the plate momentum/motion - or dents. Some of the boolits energy is dissipated in turning the boolit to dust or an irregular shape. The plate absorbs ENERGY which imparts some (much less than the boolit) motion into the plate,
Energy is related to WORK as the Prof. speaks of. Only work has time associated with it. Momentum is NOT related to work, it is a term to describe energy in motion. Time, distance, velocity, energy are measurable quantities. Momentum is an inveted math term.

[theperfessor]

That's one thing many folks forget: It takes energy to deform a bullet, and that energy is subtracted from the total energy available to transmit to the target. If that deformation makes the bullet cut a larger wound channel or transmit more energy and momentum to the target then it is usually a good tradeoff. In a handgun with a limited amount of energy available it may not be a good decision; a large, heavy bullet at moderate velocity transmits more energy and momentum than most light, fast bullets.

A light bullet that vaporizes on the face of a steel target isn't as good as a heavy bullet that deforms and sticks briefly to the target as the bullet's velocity drops to zero and the target goes from 0 to enough velocity to (hopefully) tip over.

[theperfessor]

Well, the truth is that many terms are invented math terms. I think I recall that it only takes 7 or 8 basic units to describe all known physical phenomenon. Any term or quantity that isn't part of the base unit system is a derived or invented term. That doesn't mean the term is any less real, it just means it is a quantity derived from other more fundamental terms. Velocity is really a derived term, it is characterized as a distance divided by the time it takes to traverse that distance (miles/hour or feet/second for example).

Of course the biggest and most misunderstand difference between the SI (metric system) and the traditional English system is that the SI system uses mass and the English system uses weight. There is a basic relationship between mass and weight, and it doesn't really matter which you use as a base unit as long as you understand that for some purpose you need to know and use mass to solve problems and sometimes you need to use weight.

Years ago I shot bowling pins. I used a Colt Government model in .45 ACP The load that worked best used a 255 gr RNFP that was intended for a .45 LC over a moderate load of Unique (I think). More effective at slow speed than 200 gr SWCs at any speed and 230 gr RNs. The second best bullet was a 230 gr truncated cone.

Then I got a Dan Wesson .44 mag with an 8" barrel. Wow, I could just about reach out and hit the pins with the barrel. No way I could get beat with this baby! Loaded up some 250 gr SWCs over a good healthy charge of 2400. Shot one pin 4 times within a 1" circle and the pin never moved. Found out later that there were several lightening holes about 1" diameter drilled in the interior plies. They were oriented (randomly) in line with where I was shooting and the bullets were moving so fast they simply punched through the plastic skin and two thin wood plies without even making the pins wiggle. All that energy wasted into the backstop. If I had slowed them down to 600 - 700 fps I think I would have been way better off.

[dubber123]

It's also been noted by silhouette shooters that very hard cast boolits are worse for knocking over targets than softer ones. Presumably the hard ones shatter upon impact and don't transfer energy as well to the target as a softer one. Pretty much what theperfessor says. I think.. :)

[igolfat8]

So can I assume that a soft lead bullet is a better projectile choice than say a copper plated or copper jacket of equal weight and velocity?

[fredj338]

No, it takes less work to bring a 145gr bullet to 1200fps than it takes to bring a 175gr bullet to 1200fps these two bullets will necessarily have different kinetic energy, the 175 will have more energy to transfer when it hits the target, so it will hit harder. That's the short answer, if you want to get all mathematical, go here;

http://en.wikipedia.org/wiki/Kinetic_Energy
Energy has little to do with it, it's a momentum thing. Also a heavier bullet is longer. A longer bullet stays on the target to continue driving on the plate. High speed/light bullets jst don't get it done on steel plates, unless you are talking about penetrating them.
As to jacketed or lead, I feel a jacketed, of the same wt, has a slight advantage on steel. It resists coming apart so more mass stays on target. When I used to shoot handgun metsil, I would use a 265gr jacketed in my 44mag for the 200m rams, lead for everything else.

[Doc Highwall]

In shooting to knock something over like steel rams or bowling pins, high velocity small caliber bullets that are hard bullets are your enemy, and large caliber slow moving soft bullets are your friend.


A friend of mine use to shoot a 7mmTCU with the RCBS 168 grain bullet and he found out that even though it started out at a slower velocity at the muzzle it was going faster at 200 meters due to momentum/B.C., and with the greater dwell time on the rams with a softer alloy the rams were knocked down better.

[dtknowles]

Yep Mx(VxV)

no, that is KE, for momentum the velocity is not squared.

Tim

[fouronesix]

Yes, it's momentum.

momentum is mass x velocity
kinetic energy is 1/2 [ (mass x velocity) squared ]

[cbrick]

It is indeed momentum that takes down steel targets.

Multiply the bullet weight in grains by the velocity at impact. Divide the product by 226,000 ( a gravimetric Constant).
Example: 45 caliber 240 grain bullet 200 yard velocity of 985 fps. 240 x 985 = 236400 divided by 226,000 = 1.046 pound-seconds momentum.

When figuring momentum bullet weight is worth 4 times velocity. In other words given two bullets traveling at the same velocity, one a 100 gr and one a 200 gr the 200 gr would have 4 times the momentum. To equal the momentum of the 200 gr bullet with the 100 the 100 gr bullet would need a 400% increase in velocity.

It's not necessarily bullet hardness that shatters a cast bullet on steel but what makes it hard. If you heat treat a lower Sb alloy (2%) to the same BHN as lino (12%) it won't be nearly as brittle as the lino bullet. I quit using lino in silhouette many years ago for that very reason and never left a properly set hit ram standing again. The brittle Sb bullet would have less dwell time on target than a more malleable bullet.

Rick

[RustyMusket]

Empirical learning about mass and energy...

Years ago, the corn field next to the house had been planted and it rained having exposed a round white rock about 175 yards up the hill. It had dried for 2-3 days and that rock was a tempting target. If you hit it, you saw a bit of white dust and heard the ricochet....if you missed, the puff of dirt made the miss obvious. My brother and I decided to test every rifle on the farm and we shot several 30 cals, a 35 cal, 7MM and some 16 ga. slugs. We made lots of hits and misses. The last rifle was the 50-70 Springfield....we debated because neither of us wanted to clean the BP gun.

On the third shot, the white rock disappeared from view and we could not figure it out. When we walked up the hill, a rock the size of a bowling ball was there atop the soil where the white rock had been. The 50-70 slug had hit the white face of the rock full square and imparted all its energy....rolling the rock up and out of the wet ground. We could not believe how much energy that took but it gave us new found respect for the old rifle with that 510 gr. slug.

A few years later, we used it on some whitetail depredation shoots in the apple orchards and the effect of that huge, slow moving slug on deer was astounding.

[44man]

Like Rick, I shot IHMSA a long time and never left a ram standing hit with a .44, 7BR or 7R. Heavy bullets with "dwell" time on steel.
Taken to hunting, "dwell" time is also important.
Boolits too hard shatter without leaving the momentum on the steel. It is not easy to knock 50# of steel down. Done right even a 7mm will do it.
The .44 with a 240 gr will have .99 to 1.00 momentum at 200 meters. Even the 7 TCU and 7R can reach this. Even seen 6.5's do it. .357 can be sad. ACP can leave almost any steel standing from 50 to 200.
.357 max has more then enough. Needs 200 gr rifle bullets. Velocity adds to momentum but not with the wrong bullet or weight. The bullet must hold together long enough to transmit energy.
Don't even look at steel results for hunting, far different.

[cbrick]

357 Sad? I've yet to leave a ram with my 357 but then I don't use a Colt or Smith hand grenade either, I wouldn't want to try the loads I use in the FA in either of them.

Rick

[dubber123]

357 Sad? I've yet to leave a ram with my 357 but then I don't use a Colt or Smith hand grenade either, I wouldn't want to try the loads I use in the FA in either of them.

Rick

Well, as you know loads for the F/A .357 mag are usually faster with any given boolit weight than a .357 Maximum. Being able to safely run into the rifle pressure range makes the .357 mag quite a bit more powerful. There just aren't many guns capable of doing it safely.