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How much bullet momentum (bullet weight x velocity) needed to reliably knock down targets?


Mysterious Stranger

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The OP is rightly concerned about knockdowns.  At EOT stage 9 was an all knockdown stage.  One shooter on my posse lacked ammo that would reliably tip over targets.  He had to shoot five makeup shotgun rounds to get a clean stage.

 

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- Although the .32 caliber revolvers and .36 caliber cap and ball revolvers are legal, they may not be powerful enough to handle all reactive targets.

SHB p.38 Revolver Calibers

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47 minutes ago, Edward R S Canby, SASS#59971 said:

The OP is rightly concerned about knockdowns.  At EOT stage 9 was an all knockdown stage.  One shooter on my posse lacked ammo that would reliably tip over targets.  He had to shoot five makeup shotgun rounds to get a clean stage.

 

46F34D82-6E77-4AFE-B985-CFD1358CED98.thumb.jpeg.4414ca6edf54112b6b3696be873865f5.jpeg

 

Did the shotgun rounds fired to make up for any plates left standing have to be fired at a target or just into the berm?

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31 minutes ago, Smokin Gator SASS #29736 said:

 

Did the shotgun rounds fired to make up for any plates left standing have to be fired at a target or just into the berm?

I don’t remember.  Perhaps someone else will reply.

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40 minutes ago, Smokin Gator SASS #29736 said:

Did the shotgun rounds fired to make up for any plates left standing have to be fired at a target or just into the berm?

 

A standing static target was left to aim out, but they shots did not have to actually "hit" it, just be fired at it.

 

It is the yellow MU (Make Up) target on the stage 9 schematic.

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1 minute ago, Itchy Trigger said:

 

A standing static target was left to aim out, but they shots did not have to actually "hit" it, just be fired at it.

 

It is the yellow MU (Make Up) target on the stage 9 schematic.

 

I'm getting quite a good education here today!

 

Jim G

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I really like stages with a lot of knockdowns. Then again I run 200-205 power factor on the pistols, rifle is hitting about 280. 

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Let's see what a good book has to say regarding knockdown capability, or bullet energy.

 

From: Textbook of Pistols and Revolvers by Maj. Julian Hatcher.

 

" A moving object tends to keep on moving, and the heavier it is, or the faster it moves, the harder it will be to stop. For example, a bullet that weighs 200 grains, will be twice as hard to stop as one that weighs 100 grains, and is moving at the same speed. Thus the energy of bullets varies directly as the weights of the bullets.

 

Velocity, however, works differently; If two bullets have the same weight and one is moving twice as fast as the other, it will not be twice as hard to stop as might be expected, but four times as hard. And if a bullet is moving three times as fast as another of the same weight, it will be nine times as hard to stop. Thus energy varies with the square of velocity."

 

 

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6 hours ago, PaleWolf Brunelle, #2495L said:

- Although the .32 caliber revolvers and .36 caliber cap and ball revolvers are legal, they may not be powerful enough to handle all reactive targets.

SHB p.38 Revolver Calibers

I've shot .36 caliber revolvers in CAS since 1986 using 15 grains of 3F and 77 grain round ball.  I can categorically state that if I hit a KD in the upper 1/2 or 1/3, I have not had a KD fail to fall, if they fall for anyone.  Sometimes they're REALLY slow to fall, but fall they do.   Hell, I get called for more misses on static targets than those "slow" KDs.

 

There are several things to worry about in a CAS match, but knockdowns shouldn't be one of them

 

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7 minutes ago, Lawdog Dago Dom said:

From: Textbook of Pistols and Revolvers by Maj. Julian Hatcher.

 

I remember that formula from Physics, but I also remember the well-known "Taylor Knock Out Index" which was developed by John Taylor, an extremely experienced African hunter. His formula was based on killing thousands of large game animals with nearly any caliber you can imagine. His formula also adjusted for the bullet diameter and referred to it as the "power yardstick" for African rifles. 

 

The Taylor KO factor multiplies bullet weight (grains) by muzzle velocity (feet per second) by bullet diameter (inches) and then divides the product by 7,000, converting the value from grains to pounds and giving a numerical value from 0 to ~150 for normal hunting cartridges.

 

Basically, it says that everything else being equal, a bigger impact circle equals a better knockdown capability! I agree with that, but I have never understood why he didn't take into account the exponentiality of the velocity!

 

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13 minutes ago, Griff said:

...There are several things to worry about in a CAS match, but knockdowns shouldn't be one of them

 

Except for actually hitting them, since most plate rack targets are a LOT smaller than the average huge pistol target.  :)

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22 minutes ago, Lawdog Dago Dom said:

Let's see what a good book has to say regarding knockdown capability, or bullet energy.

 

From: Textbook of Pistols and Revolvers by Maj. Julian Hatcher.

 

" A moving object tends to keep on moving, and the heavier it is, or the faster it moves, the harder it will be to stop. For example, a bullet that weighs 200 grains, will be twice as hard to stop as one that weighs 100 grains, and is moving at the same speed. Thus the energy of bullets varies directly as the weights of the bullets.

 

Velocity, however, works differently; If two bullets have the same weight and one is moving twice as fast as the other, it will not be twice as hard to stop as might be expected, but four times as hard. And if a bullet is moving three times as fast as another of the same weight, it will be nine times as hard to stop. Thus energy varies with the square of velocity."

 

 

 

No, that is not QUITE correct, despite it being Julian Hatcher's opinion at the time.

 

He was absolutely correct about the weight of the bullet being ONE factor directly proportional to the FORCE it transmits to anything it hits. The other factor is bullet velocity. And indeed weight x velocity ( which is same as what we now call "power factor" except different units of measure) but physicists call "momentum", is indeed a valid measure of how much momentum is imparted to whatever the bullet hits.

 

But the second paragraph is not QUITE correct. It IS true that the MANstopping ability of  a bullet IS proportional to mass x velocity squared. That is why a 357 Magnum 125g bullet flying at 1500 fps (625 ft lb of energy) stops an assailant way more reliably than a 45 ACP 250g bullet flying at 900 fps (450 ft lb of energy). But that's because the 357 dumps more ENERGY into the assailant's body, and that energy disrupts body functions dramatically. Just like a good jolt of electricity, or a laser beam, can disrupt a human body internally. And this is why a .tiny 223 caliber 69 grain bullet bullet flying at 3000 fps (1400 ft lb of energy) is a preferred military weapon.

 

But knockdown targets are different. A bullet hitting a knockdown target is like a billiard ball hitting the side of the pool table or another billiard ball. No internal disruption occurs. It's simply one moving object colliding with a rigid and impenetrable solid block of material that is basically unchanged aftyer the collision, except for having been MOVED. Any physicist will tell you that this simply results in a transfer of MOMENTUM, not any meaningful amount of energy internal to the body that was hit.

 

This was actually taught in high school physics when I was in high school, actually using  the billiard ball analogy as the visual for the physics.

 

The RIGIDITY of the bullet does have an effect though, beyond everything I just said. IF the bullet is very HARD it does not deform very much when hitting the knockdown target. So, the momentum transfer is, in terms of Physics, quick. This is important, because momentum transfer occurs as (Force x Delta T) where Delta T is the TIME required to complete the collision process. The shorter Delta T is, the greater the Force transmitted.

 

But if the bullet is SOFT (for example an unjacketed and SWAGED bullet), the collision process is NOT rigid and quick. Instead, the bullet starts deforming on impact. This results in a Force x Delta T where Delta T is LONGER and Force is therefor SMALLER. A significant portion of the momentum (mass x velocity) is converted into "wasted energy" that is consumed to deform the bullet and to heat it. 

 

So, if you want to maximize the knockdown ability of a bullet with any given weight and speed, use a HARD bullet, not a soft one.

 

Of course, a jacketed bullet does an even betetr job of knocking down a target, but jacketed bullets are not allowed in CAS specifically because they don't deform nearly as easily, but rather tend to bounce BACK at the shooter. i.e. they are much more like the perfect "billiard balls", and that makes them dangerous in our game.

 

I myself am violating that bullet rigidity rule for best knockdown ability, by using a swaged bullet, but I have my reasons for doing so:

- I want the quality and consistency of a swaged bullet

- I plan to compensate for the softer more deformable bullet by making it fly a bit faster.

 

But this is why I asked the question that started this thread. I didn't know how MUCH more speed I needed.

 

Jim G

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Whether it's higher math or my blood pressure, I have a headache reading that!  All I know is that if one studies the various manufacturers' load data, a Standard 158 grain 38 Special has less velocity than the same manufacturer's "Cowboy" load.    I.e. Winchester's standard 158 grain .38 Special load is stated as having a MV of 775 fpts.   Their "Cowboy" loads of the same weight are stated as having a MV of 800 fps.  The additional 25 fps is overkill.  You're way over-thinking this.  While pistol and rifle KDs are not uncommon, they're far less numerous than warrants this much study.  

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4 hours ago, Abilene, SASS # 27489 said:

Except for actually hitting them, since most plate rack targets are a LOT smaller than the average huge pistol target.  :)

 

Most of the revolver or rifle knockdowns I've seen are the plate racks with targets spaced apart or the tombstone type with smaller plates behind the first plate. With either setup it commonly allowed 10 shots, both revolvers or 10 shot rifle, to knockdown 5 plates. Misses on the plates wouldn't count unless left standing. However many shots it took to knockdown the plates the remaining shots would be on a dump plate where misses would count. 

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Just shoot fast. Knockdowns are few and far between. You do not see the 60PF guys worrying about it, they are shooting 12 second stages. 
 

Accurate guns are interesting but these do not typically dangle at the end of your arm. Handguns are point and shoot and you may be surprised to find they hit closer to center at speed. 
 

If you want to shoot over bags get adjustable sights. If you insist your point is valid you already have your answer. There are a bunch of CAS shooters using slip on sights which are probably not regulated. 
 

Or simply file your rear sight notch on the right side until the bullet impacts where you want when centered. 
 

Good luck

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Knock downs are what the 44-40 does best for me!! Even marginal hits knock down with my 200 grain bullet.

 

Bugler

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Oh, oh. I got to the local CAS range yesterday and while there, I examined the knockdown target setup, and see an issue given the lefthand windage error in both of my Cimarron revolvers.

 

The knockdown target assembly has 5 (good) round targets on it, and they are 8" diameter (also good).

 

There is also a nice "saloon bar" at the firing line at that point, so I guess you "belly up to the bar" to shoot at the knockdown targets.

 

But, the entire assembly is WAY too heavy to be easily portable. I tried picking up just one end of it and was unable to do so. It seems like it requires a machine, not humans, to lift and move it.

 

I measured distance from the bar to the knockdowns, and it is 17 yards. So, it sounds like our local club (which I joined last fall just before it shut down for the winter season) has its knockdown placed at a longer distance than what the above thread discussion implies is "typical".

 

As I mentioned earlier, both of my cimarron Model Ps in 357 Mag caliber shoot left of POA, one by a bit over 2" and the other by about 4" at 25 yards, because the sights are physically off (recently proven by a laser boresighter). So, at 17 yards, these 2 revolvers will shoot respectively 1.4" and 2.8" left.

 

I fired 1a total of 5 shots in 3 strings at the knockdowns, and with the combination of windage error, and also elevation error, coupled with the circular shape of the knockdowns, I experienced only 1 miss (no ringing of the target), but also 4 shots where the target rang but did not fall, presumably because I hit at a point where there was insufficient leverage to actually cause the target to pivot enough to fall. I was trying to shoot somewhat right and high on the targets to attempt to compensate for the windage and elevation errors.

 

These shots were all fired with a Trail Boss load of 4.1 grains that produces muzzle velocities in the 830 to 850 fps range with a 158g swaged lead bullet.

 

Is 17 yards unusually long for knockdown targets?

 

If the 17 yards is not unusual, I am going to have to do something about the sight errors, especially the windage. While I can probably find a suitable consistent sight picture with the front sight slightly elevated to compensate, the different windage error on each handgun would require remembering which is which during a rapid fire string, and I don't like that when there are already a number of other important things to remember and monitor.

 

Jim G

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17 yards with 8" knockdowns in Cowboy setting means those were set as Rifle targets, not Revolvers.     8 yards would be a stretch for revolvers for most cowboy matches.  Then again, perhaps it was set for Wild Bunch, where pistol shots at "cowboy rifle distances" are more common.

 

Hits on targets that wiggle the steel without knocking it over indicate hits well off the vertical centerline, and/or a loose or only one hinge pivot.  KDs collect lots of lead splatter and some KD designs let that splatter collect right in the hinge, making it harder still to knock it over.

 

good luck, GJ

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