Would a 12 Gauge Slug Knock You Over While Wearing Armor?

I remember one episode where the recoil absolutely would knock the shooter down, but the targets still barely moved. There was no armor involved though and the "gun" was a pirate cannon firing a 6 or 8 lb ball. The ball went through several pig carcass targets and they barely moved. The force needed to tear living or recently dead tissue isn't enough to move the target very far, if at all, except in certain unusual cases.

I was surprised by a racoon in my garbage can.
I swear I flew backwards like a stuntman getting both barrels.

Living beings react a lot different than stumps or blocks.

"Energy has to be conserved too. Where did the difference in energy go?"

Here is the crux off understanding the problem I think. Momentum is conserved in that the momentum of the gun and the bullet and ejecta is the same. Total energy mass energy of the process is conserved. But......there are a lot of individual components of energy to be totaled and each of those varies according to the process. Basically the chemical energy of the powder burn is transferred mostly to the bullet and gasses in the form of kinetic energy. There is also heat energy that is dissipated. And some of the chemical energy is transferred to the gun as kinetic energy but fortunately only a small portion. So the bullet ends up carrying most of the kinetic energy. This is fortunate for the shooter.

So the energy is conserved in the sense that the total energy is limited to what the powder can produce but the energy of the gun and the bullet are not the same. The momentum of both is the same. Thus the energy has to differ proportional to the square of the velocity of each.

LookAtYou said:

So how do you factor in the weight of the gun itself, the stock/padding for the shoulder, the fact that the slug has a smaller impact area than the stock of a firearm, and other things that might alter the force felt on the shooter vs the victim?

It seems a gun is designed to mitigate some blowback force on the shooter, while the person getting shot has none of that.

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What about it? The amount of force will be the same; yes one might be spread over a slightly larger area so the FELT recoil seems less; but the actual force is the same. Hollywood has folks convinced that people getting shot go flying backwards - it simply isn't true

DukeConnor said:

I was surprised by a racoon in my garbage can.
I swear I flew backwards like a stuntman getting both barrels.

Living beings react a lot different than stumps or blocks.

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Orrrr conversely he JUMPED back in fear and pain. Think of how you likely react to sudden, unexpected pain or impact. You likely flinch like the bejezzus and recoil away from the source of unpleasantness. It like a deer who gets shot and LEAPS AWAY running for some distance before falling.

Physics is physics. A small projectile and a 12 gauge slug is a small projectile technically, doesn’t have the kinetics to knock you on your butt. YOUR natural human reactions whether through disruption of one of your mechanical, hydrolic, or electrical systems or simply your shock / pain reaction might very well put you on the ground or seem to push / stumble you back but those things are the ancillary effects of getting SCHWACKED by a projectile.

Now if the slug was fired from the passenger seat of a dump truck that subsequently runs into you then yeah......probably a solid 10 or 15 feet back.

If you shoot a slug from a shotgun & not braced for it, it will knock you back or down, so if you get hit with a slug & not braced for it it will do the same. It that old physics thing an object at rest will try to remain at rest & the object in motion will try to stay in motion until it hits the object at rest. LOL

It was an eye opener when back in the late 60's I shot a rifled slug at a car door. Found a big dent and mushroomed slug on the ground about 3 feet in front of it. It was a 63 Ford station wagon door though. These days it might actually go through a car door though. The 00 Buck went through both passenger and drivers doors however.

Local grocery store clerk took a load of buck shot from a ten inch barrel in a IIA vest and went with down. the shot was still in the wad when it hit having been fired with the muzzle between one and two feet away.

He commenced screaming that he was about to die and the stake out team cut off his shirt and armor. He actually had a broken rib and awful bruise and I bet it hurt as much as he thought. He did fall back but most believed it was a reaction to get away from the gun before a second shot.

The vest, with a couple of pieces of shot stuck to the fabric, got framed and hung in the dressing room to remind officers to put on their stinking hot vests.

-kBob

Draw your own conclusions
Simple MV = mv physics

theotherwaldo said:

If firing the slug from an eight pound gun wouldn't knock you over, why would taking the impact on an eight pound (or more) piece of armor knock you over?

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+1, Simple Physics

Harry

LookAtYou said:

Thanks, very informative! Also, don't certain factors play a part in effecting the force felt by the shooter vs the victim. Like the shotgun absorbing some force itself (recoil?), the stock/padding, etc?

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This will get long, so hang in there.


Yes, certain factors DO play a very important part in affecting the force felt by the shooter vs. the victim.

Always remember: momentum transfer is conserved in a closed system.


What affects the force felt by the shooter?

All other things being constant, the mass of the shotgun and the length of travel of the shotgun in recoil over time.

If you shoot a heaver shotgun, the force felt by the shooter "feels" less than for a lighter shotgun.

If you use a padded butt on the stock, you can reduce the felt recoil because it effectively lengthens the recoil distance traveled, as well as the time in which the distance is traveled. Remember...force is mass times acceleration. Acceleration is change in velocity divided by change in time. If you take a longer time to drop the recoil velocity to zero, then acceleration goes down and the force felt decreases.

What affects the force felt by the shooter?

Again, all other things being being constant, it's force which is equal to mass times acceleration. (And in closed system, momentum is conserved. I keep saying that, it seems!) So what affects the force felt by the victim?

The same things that affect the force felt by the shooter. Mass of the slug and how quickly the slug velocity drops to zero, because that affects the acceleration of the slug...and therefore the acceleration of the combined mass of the victim and the slug (because momentum is conserved). The velocity question is where it gets difficult because you have to make some assumptions.


Here's an apt analogy that's very easy to visualize:

Ever play pool or billiards? All the billiard balls (including the cue ball) are of the same mass. If you line up a perfectly straight (head on) shot with your cue ball and the 8-ball, what happens to the two balls when they collide?

The cue ball stops and the 8-ball moves off at the same velocity the cue ball had initially.

If the two ball could, somehow, "stick together" on impact and the table was a frictionless surface, what would happen? The combined mass of both the balls stuck together would move at 1/2 the initial velocity of the cue ball. (Because momentum is conserved.)


Now...imagine what would happen if you had a billiard ball that was 2881 times the mass of the cue ball. For the same scenario:

Head on shot: The cue ball hits the far more massive 8-ball and bounces back with ALMOST the same velocity it had initially. Some momentum would transfer and the 8-ball would move with a very tiny fraction of the initial velocity of the cue ball.

If they stuck together on a frictionless surface...the combined mass of both balls would move together at a tiny fraction of the initial velocity of the cue ball.


Remember...momentum is mass times velocity, and momentum is always conserved in a closed system. So, using the same numbers above slug/victim scenario ("1" for mass of the cue ball and "2880" for mass of the 8-ball):

Initial momentum of the 8-ball is zero because it's initial velocity is zero. (m8v8 = 2880 times zero)

Initial momentum of the cue ball is mcvc, where it's initial mass is "1" and initial velocity is whatever you choose it to be.

Final momentum is m8v8 plus mcvc. Now the final mass will be 2881 and their final velocity will be the equal (because they're stuck together and therefore traveling at the same velocity). We can say the equation for this is mfvf.


Therefore the final momentum is equal to the sum of the two initial momentums (again...this is where it's important to remember that momentum is conserved in a closed system):

mfvf = m8v8 + mcvc

Remember...m8v8 is zero because the massive 8-ball is stationary. So it drops out.

mfvf = mcvc

Therefore final velocity (vf) would be:

vf = (mcvc) divided by mf.

OR

vf = (mc/mf) times vc = (1/2881) times the initial velocity of the cue ball.


BACK TO YOUR SCENARIO:

Since I conveniently used the same mass, let's assume the initial velocity of your 1 ounce slug is 1,760 fps.

Dividing that by the total mass of the victim plus the slug (2881), you get a combined final velocity of the victim being 0.61 fps (which is about 0.4 mph).

BUT...FORCE is equal to mass times acceleration. This is what the victim would "feel". Acceleration is change in velocity divided by the time it takes for that change to happen.

For simplicity, we can assume that 0.61 fps is effectively zero compared to the initial slug velocity of 1,760 fps. So the change in velocity will be 1,760 - zero = 1,760 fps.

How long does it take for the slug to decelerate to zero fps? I really don't have a clue. And therein lies the problem. Objectively speaking, it's definitely not a long time. A fraction of a second, to be sure. It would be interesting to see if anybody has done any experiments for something like this.

But the bottom line the force is directly proportional to how fast that 2881 ounces is "pushed" to a velocity of 0.61 fps. The less time it takes to accelerate the victim to 0.61 fps, the more force the victim will feel.

Read the various attempts to dispel the myth pushed out for years by popular entertainment regarding the impact of bullets, shotgun pellets, rifled slugs... The best demonstration that I ever saw or read about was included in the book Street Survival that came out in the late seventies...

Researchers placed a man sized dummy on a wooden platform with rollers on it. The weight of the dummy was nearly 200lbs if I remember correctly and it was so easy to move on that platform with rollers that it could easily be moved with a single finger’s push...

A close quarters shot using a 12ga with buckshot didn’t move the dummy at all despite the dummy absorbing every pellet (no pellet penetrated all the way through). So much for movie myth...

The effects on a live body protected by body armor from a rifled slug or other substantial projectile? Considerable, but no worse than being struck by a fast pitch hardball or other blunt force trauma that is not allowed to penetrate the way it would if you were not wearing that “hot stinky vest”... Hot and stinky is a very accurate description of body armor worn daily by the way ( ask me how I know...).

This from a guy that wore a vest for nearly 22 years down in south Florida... My first vest, an early Second Chance model I had to buy myself before my Department began issuing them...was always part of my gear even during day shifts in August...

Equal and Opposite reaction. If it were to knock over the wearer, that means it would have already knocked over the shooter. Only in movies.

Physics are not exactly my forte, but the idea that the guy firing the gun is receiving the same energy as the guy being shot doesn't seem quite right to me. There is a lot of energy being released, and not all of it would just go straight back through the shotgun I can't imagine.

It would depend on if you were in front, or behind the car and house it blew up before hitting you. Thats my Friday night answer.

RetiredUSNChief said:

If you shoot a heaver shotgun, the force felt by the shooter "feels" less than for a lighter shotgun.

If you use a padded butt on the stock, you can reduce the felt recoil because it effectively lengthens the recoil distance traveled, as well as the time in which the distance is traveled. Remember...force is mass times acceleration. Acceleration is change in velocity divided by change in time. If you take a longer time to drop the recoil velocity to zero, then acceleration goes down and the force felt decreases.

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The first sentence is about actual recoil; the second is about felt recoil - two different animals

demontfort said:

Physics are not exactly my forte, but the idea that the guy firing the gun is receiving the same energy as the guy being shot doesn't seem quite right to me. There is a lot of energy being released, and not all of it would just go straight back through the shotgun I can't imagine.

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No, they aren't, but Newton's Third Law hasn't been repealed yet. The difference is the weight of the one force (gun acting on shooter) vs. the weight of the other force. (Slug acting on target.) The heavier the gun is the lighter the percieved recoil is. (There are other variables involved. A semiauto spreads the reaction out over a longer time, milliseconds though it may be. A stock with more area on the body will give less perceived recoil, as will recoil that is straighter to the axis of the bore.) Contrast this with an 8 pound (128 oz.) gun and a 1 oz. slug . The 'felt recoil' of the shotgun is 1/128th of the 'felt recoil' of the slug, in simplistic terms. Felt recoil of a slug (on the gun end) is @20-24 ft. lbs. So at 24 ft. lbs at the gun this gives the slug @ 3,072 ft. lbs of energy (this is called "muzzle energy", because it of course drops off over distance because because velocity is dropping) but at close range, this is a considerable amount of force to be concentrated in a flying spherocylinder with a width of just under 3/4". Consider that the M.E of a 125 gr. HP .357 Magnum pistol round is 583 ft. lbs. The slug is just over 5 TIMES the muzzle energy of the .357's most effective round ( according to Sanow and Marshall)
All that energy is still not enough to pick up and man and fling him across a room. On either end. Although I will state that from personal experience, if the buttstock is not on the shoulder when the shotgun is fired, it will feel like you got the other end of the equation!

LookAtYou said:

So although not guaranteed to lift or knock a man over, I guess that 3000+ Ft/Lbs energy, stopped by armor, would hurt like whistling dixie? And maybe kill the wearer?

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Depends on the armor.

LookAtYou said:

So although not guaranteed to lift or knock a man over, I guess that 3000+ Ft/Lbs energy, stopped by armor, would hurt like whistling dixie? And maybe kill the wearer?

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Fluid dynamics being what they are, and the human body being rather fluid in nature, the armor converts what would have been penetration and the resulting wound channel into blunt force trauma that while survivable (more than likely) does not make it painless. High hits would likely collapse lungs, break sternums, possibly fibrulation, low hits could cause visceral bleeding, hiatial hernia, liver damage, etc.

I couldn't find it when I looked, but I remember seeing a You Tube of someone shoot a IIIa vest wrapped around a block of clay; the slug did not penetrate, but when they took the vest off the imprint of the "blunt trauma temporary cavity" , it was quite an impression. (pun intended) Bear in mind clay is more solid than the human torso.

Two additional things to consider about body armor...
The first is that there are still far too many vulnerable parts of you available to incoming rounds when wearing that vest and body armor that you can actually wear day after day won’t hardly slow down a rifle round... I lived with that knowledge all the years I wore the armor.

Secondly is that getting hit by a substantial incoming round is not only painful but might just either slow you down or actually stop you from responding to additional armed action by a determined aggressor... That’s a very bad place to be. That’s the main reason I wore the additional shock plate that came with the vest I wore. I was hoping it would eliminate enough of the blunt trauma of an incoming round, allowing me to stay in the fight... Very pleased that I never had to learn about that stuff first hand in my career.

Most of my knowledge about body armor was learned the hard way, with daily wear. Some of it was learned from the area I was in. Every year, for all of my years, 3 officers a year were killed on the job in the combined area of Dade and Broward counties... for those not familiar with south Florida that’s the Miami and Fort Lauderdale areas together (pretty much solid urban or suburban for 70 miles of coastline...).
All of us, the law enforcement community, were very aware of the circumstances in each case. Me, I quit going to funerals early in my career... More than a few of the officers killed were wearing body armor when they were killed. On the plus side of things more than a few officers involved in horrific traffic crashes on the job were saved by the vests they were wearing at the time...

Once again, very glad to be out of that world..

Just for grins and giggles, let's ramp this up to an 8ga shotgun. In "Cowboy" times, the 8 ga. was readily avalable and used. After anything larger than a 10 ga. was illegal for waterfowl, the 8 and 4 ga. fell out of favor. Wonder what a "pumpkin ball" from one of them did to old tome critters/people.

I lnow yhey didn't just gtab their shoulder and keep on shooting.

PWC said:

Just for grins and giggles, let's ramp this up to an 8ga shotgun. In "Cowboy" times, the 8 ga. was readily avalable and used. After anything larger than a 10 ga. was illegal for waterfowl, the 8 and 4 ga. fell out of favor. Wonder what a "pumpkin ball" from one of them did to old tome critters/people.

I lnow yhey didn't just gtab their shoulder and keep on shooting.

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Why not go up to grape shot then?