Please explain "knock down power"

[9mmMike]

OK team,
I have been struggling with this for a while. I have a good friend who is a math weenie. He contends that the force with which a 12 Ga. slug strikes a BG is no different than the force that SG stock applied to your shoulder when it was fired.
He does not argue that the damage from the slug will drop a BG.
He does question the claims that a BG wearing bodyarmor would be physically knocked backwards or down from the energy of the shot.
I have also read such claims about the effects of slugs (and buck) on bodyarmor but I have never seen any real evidence. It's kind of like the guys that post about the Navy Seal that their brother's best friend knows.......
Can someone explain, small words please, to me how a slug can have enough energy to physically knock a full grown man, wearing body armor, down?
Thanks in advance,
Mike

[fix]

It doesn't happen. I have never experienced it personally, but I know a cop who took a 20 ga slug to the chest while wearing a vest with a ballistic plate. Broken ribs, cracked sternum, broken collarbone, and a HUGE bruise. He said it felt like a Randy Johnson fastball, but it only caused him to take a step backwards. Of course, he fell down after that, but that was because of the "oh sheeyat, I got shot!!!" factor.

[stick]

Yep, those physics laws apply. The energy the target hitting the BG is pretty darn equal to what your shoulder feels. Can a slug knock a BG down...YEP.

Why? Several reasons depending on the situation. Psychological reaction to getting shot (think: suprise-stumble-fall). Another and my favorite: it's like getting punched REALLY hard. A whole lot easier to stay standing after getting punched in the shoulder than in the gut.

[Badger Arms]

I beg to differ. While it won't knock you 10 feet backwards, imagine standing straight up without leaning and firing a 3" Magnmum slug load. It WILL knock you over unless you step back or do something to stop yourself from falling. Ever watched somebody firing a shotgun... it's alot of force.

Unfortunately, Hollywood has implanted fantasies in the minds of many where you see shotguns blanks being fired in stylized action scenes by big actors. To simulate recoil, they often just lift the muzzle on the gun. This doesn't give you a true impression of how much force is involved.

Couple this with the fact that the person we are talking about has JUST BEEN SHOT. There's not too much thought of compensating going throudh the mind of the 'animal' when this happens. On a 4 legged beast, the movement is hardly noticeable. You can generally see the shock wave go through the animal. Never have seen a running animal get hit but I'd imagine it would cause it to skip a step or two and perhaps fall just from the impact.

It's not the energy of the bullet that causes the animal to get knocked down unless you completely incapacitate the nervous system with the shot. It will however 'tip' an unbalanced human over all other factors being equal.

[Oleg Volk]

I've shot small game (rat-sized or blackbird-sized) with 22, 9Luger, 8mm Mauser and 308. Not ONE of the critters died the way people do in movies. Some muscle movement persisted for a minute or more, though it was involuntary. So guns aren't perfect "stoppers" on anything larger.

Shotguns stop by breaking structures of the body. It isn't the shot energy but the damage to organs and skeleton. The mechanical work also uses up energy which, ina perfectly inelastic collision, would have moved the object. A shotgun slug fired at a 3lb steel wedge would lift that wedge and throw it several feet. However, even that collision deformed both the slug and the steel chunk.

[C.R.Sam]

Recoil moves shooter more than slug moves target. Gun does not penetrate shooter (much), therefore all the energy is used in push. Slug penetrates and expends energy over a longer period, less push at any given moment.

No appreciable knock down power with hand or shoulder fired weapons........untill we get insanely big and recoil compensated guns.

Sam

[The Plainsman]

Keep in mind, Mike, that a fair amount of the energy created by the "blast" and exerted toward the shooter, is absorbed by the inertia of the gun itself. That's why larger, heavier guns tend to have the same or even less perceived recoil than smaller calibers - smaller caliber guns tends to be lighter and therefore absorb less energy through inertia. Net result - more "kick".

Now, exert ALL that force, going the opposite direction, into one relatively small hard object. That slug hits a small area with ALL the energy that the shooter AND his gun, just absorbed. That will either knock a person down or make them wish they had fallen down.

[ronin308]

To add to what Sam said: Imagine hitting a guy with the flat side of an oar in the chest using 20 lbs. or pressure. Then use 20 lbs of pressure with the point of a knife. The knife won't knock him back nearly as much as the oar.

[Chuck Graber]

Plainsman,
You are only partially right. The heavy gun does not absorb the recoil. The gun will eventually transfer all of it's energy to the shooter. It spreads out the impact over a greater length of time. A shooter is not injured because they absorb the recoil over about a quarter of a second. The BG takes the energy in about 1/1000th part of a second. The shooter also has a much larger area to absorb the recoil ( the recoil pad) as opposed to the fraction of a square inch that is the end of the slug.

I would say that Stick has it about right that a lot of the knock down power is a moderate amount of imparted energy and a lot of buckling of the knees. Judo and other martial arts teach that it is much easier to throw a person if you can get them off balance. The noise and the idea of being shot as well as the pain are enough to de-stabilise anyone. Therefore it often does not take much imparted engergy to drop them.

Chuck Graber

[Schweizer]

Chuck Graber:

You are also only partially right. It is true that the accleration time of the bullet(s) makes the difference. Think of a car accident: it's no problem to acclerate from 0-60 in 10 secs, it only gets bad when you hit a wall and therefore de-acclerate in a split of a second.

Concerning the size of the impact area you are wrong. Actually it is the other way around when it comes to knock-down power. The bigger the area the better and faster the energy is absorbed. The smaller the area the deeper the penetration of the bullet and therefore the longer the stoping time. (A longer stoping time means less force.) The knock-down power would further decrease if the bullet would over penetrate and therefore waste the remaining part of its energy on a differnt target.
The reason why a larger shoulder pad reduces the felt recoil is because the force pushing against your shoulder is distributed over a greater area. But the energy you have to absorb is excactly the same as with a smaller pad. If you would use a needle instead of a pad the recoil would kick you less but the needle would penetrate your body and hurt you more. Since the penetration would allow the gun to distribute the recoil over a longer distance the force pushing you would be smaller even though the energy would still be the same!

I have to add that knock down power to me means "making the target fly through the air - movie style" and not the effectiveness of disabling an attacker with the greatest reliability where bullet penetration might be a desired effect.

[JosephBoeckner]

my long lost chuck! haha this is Joseph from ellis county shooting sports, that has to be u, the same name and all, hows it going?-just now noticed ur name