Interesting physics statement...

[BigFatGuy]

Saw this on a pistol training DVD (Thunder Ranch, I think).

It's one of those things that's so clearly true, but I never thought about it enough to draw the connection.

If any round, fired from any handgun, was strong enough to knock the target down with a single shot, then the kickback would also knock down the shooter.

Equal and Opposite...

[bbguns44]

Only if the target is the same weight as the shooter. There's also some frictional
loss & thermal loss.

[BigFatGuy]

Only if the target is the same weight as the shooter.

True... (This makes me happy, being as I am, in fact, a big fat guy. ;-)

There's also some frictional
loss & thermal loss.

all of which would make the shot hit the shooter harder then the target, since the round would be going slower at the far end of the shot.

There's also elbows and wrists to consider, the shooter has some shock-absorption built in... but there's a great deal of logic in the statement nonetheless.

[bohoki]

i did an experiment

i took a 12x8 sheet of 1 inch steel plate with little steel feet and shot it with my 50 bmg it fell back and slammed against the ground skidding a bit with my lead core bullet stuck in it like a micro meteorite


i then took the same plate and put it behind the buttplate and pulled the trigger

and it barely moved

of course this was not scientific and i did hit a big higher than center on the plate than the buttplate was resting

but if anybody has shot a prarie dog with a 223 and watched it fly backwards cartwheeling you would have to assume that the little critter wouldn't have flown like that if it pulled the trigger
and it

[bigmike82]

It's not quite that simple.

There's a lot of mass being ejected from the pistol, along with the time-differential involved with the bullet's acceleration down the barrel.

It all involves the conservation of momentum, energy transference, impulse calculations...

You can shoot a 500 gr round out of a S&W .500 revolver. Will that knock you down, if you're on the receiving end? Probably.

Will it knock down a good and prepare shooter?

No.

[ir0nclash86]

Thought I saw this on Mythbusters and I found this on youtube.

starts around 3:43

[BigFatGuy]

There's a lot of mass being ejected from the pistol, along with the time-differential involved with the bullet's acceleration down the barrel.

Without looking up some equations (I'm not in the mood to do math right now), all I can contribute is this: we look for roughly a foot of penetration in human flesh from our rounds, yet the same round accelerates out the barrel within 6" or less. This, too, would seem to be on the side of the target.

I guess I'll have to dig up some equations at some point... sigh...

[bigmike82]

Yes, but is the gun forced into your body one foot?

[shy 7th]

i did an experiment ...

i then took the same plate and put it behind the buttplate and pulled the trigger

and it barely moved
...

Did you also account for the weight of the gun?
Was the gun suspended or on a rest/bipod?

I believe Newton's Third Law of Motion requires two bodies to be equal. In your first experiment you had energy from the blast transferred into the plate from the bullet. In your second experiment, you had the same energy (assuming you used the same load) transferred into the plate+gun+rest/bipod+ground/table.

I believed what you experienced would be similar to why a shooter will feel less recoil using a fullsize, metal-frame pistol vs. a polymer subcompact granted the same caliber and bullet weight.

[stix213]

Stance and balance also play into it. When you fire a gun your body is positioned to absorb the recoil. If you shot a person, they are unlikely to be positioned in a purposeful stance to absorb the hit. You're also absorbing a lot with your arms and joints. Not all of the recoil energy is being transfered from your arms to the rest of your body.

[BigFatGuy]

Yes, but is the gun forced into your body one foot?

That actually works in the target's favor... the force/second value (essentially, the aceleration of the round) is faster on the shooter's end then on the targets.

Which, ironically, might just mean that those Extreme Shock (Ultra Shock?) rounds MIGHT have more knockdown force, since they do not penetrate as deeply, and thus impart more of an impulse on the target

[bigmike82]

"Which, ironically, might just mean that those Extreme Shock (Ultra Shock?) rounds MIGHT have more knockdown force, since they do not penetrate as deeply, and thus impart more of an impulse on the target"
Right.

Which also suggests that if the round splatters on Kevlar, the knock-down power is even greater (because the momentum of the bullet is transfered completely to the body over a larger surface area, rather than penetrating).

Also think of this. If you push a guy and he falls over, do you automatically fall over because he did?

No, of course not. It's a very complex physical relationship.

[BigFatGuy]

Which also suggests that if the round splatters on Kevlar, the knock-down power is even greater (because the momentum of the bullet is transfered completely to the body over a larger surface area, rather than penetrating).

Never been shot in Kevlar, thankfully, but I've read the vest compresses several inches into the chest cavity when it stops a round... (I don't believe that considers ceramic plates)... and, for all I know, being shot in Kevlar DOES do a better job of knocking you over. I truly have no experience in the matter.

Also think of this. If you push a guy and he falls over, do you automatically fall over because he did?

if he was roughly my size, and I wasn't lunging at him, but rather we stood toe to toe and just pushed... I very well might! When you shove someone you lean into them, that's what stops you from falling.

[bohoki]

i do not believe any handgun has the force to knock one down, people get shot and they fall/collapse

or due to reflex they may fling them self in a direction away from the shot

i guess it has to do with pounds per square inch and impact over time

[shy 7th]

...
Also think of this. If you push a guy and he falls over, do you automatically fall over because he did?

No, of course not. It's a very complex physical relationship.

In most cases when one person shoves another or likewise, when a boxer punches his opponent they are transferring inertia.

Think of one billiard ball striking another. The cue ball transfers its energy to the second ball and then comes to rest. The second ball continues to the pocket.

This is Newton's First Law of Motion (also Galileo's Law of Inertia). This is different from the explosion happening inside the chamer of a gun.

In the case of the gun, the energy projecting the bullet forward is at the same time projecting the shooter backwards. The discrepancy of mass is why the bullet goes so far forward, so fast and why the shooter stays put.

Of course, when the bullet stikes its target we are again talking about my billiard balls example. The bullet transfers its energy into the target. The same energy imparted on the shooter. So if the target were wearing a kevlar vest and all of that energy were transferred to the target, it should be no worse than what the shooter experienced.

A very complex physical relationship, indeed.

if he was roughly my size, and I wasn't lunging at him, but rather we stood toe to toe and just pushed... I very well might!

This is a better analogy of The Third Law.