Am I missing something here? Put the butt of a high-powered rifle up to your head and go about your daily business. Then, have someone pull the trigger when you least expect it and see if your head doesn’t “snap back violently.” In other words, I think you are missing the fact that while the “kick” of a gun isn’t as damaging as the bullet, they do kick.
I saw a clip on some “Banned From TV” video where a guy in (South America?) was walking out of a building in which there was apparently some sort or (riot?) going on. The guy didn’t seem to be doing anything wrong but a (cop?) in riot gear blasted him almost point black in the chest with what appeared to be a 12-gauge shotgun. That guy “went flying.” Maybe you people have just never fired a shotgun or a rifle before? It’s not uncommon for them to leave bruises on your shoulder.
The difference being, in that case 100% of the energy would transfer to your head. In Kenedy’s case, very little energy transfered (The bullet went more or less clear through).
Plus, when a high-powered round like that hits, it tends to explosively “eject” material from the target, giving force in the opposite direction. From what I’ve been told, it’s almost as common for a target to fall -towards- the shooter, as away.
And I’ve seen video of a single person getting absolutely -pummeled- with beanbag rounds, and barely even budged by it. A shotgun has slightly less energy than a hunting rifle round (about 2/3s, I think), IIRC. However, with buckshot, you wouldn’t have to worry about loosing energy to overpenetration. In any case, what you’re describing is likely a psychological reaction to getting shot. A shotgun just doesn’t have enough energy to lift a man up off the ground (Try shooting one straight down, if you want… Or hold the buttstock against your chest, stand straight up, and fire. A shotgun -will- cause a person to go off-balance, however. When getting shot, it’s quite likely that the combination of shock and momentum will cause the person to fall over… Some people might even react psychologically by trying to curl into a fetal possition when they get hit; Combined by the (slight) momentum imparted by the hit, it might make it look as if they were blown off their feet… The mind factors greatly into it.
But “send him flying”? No. It’s the same force on both the shooter and the target, so if you fire a round powerfull enough to send that person “flying” (And barring any bracing of the weapon, or a super-heavy gun), you’d go flying as well.
And I have to admit, of the (admitedly, relatively few) hunting rifles I’ve fired (.270 and .30-06), I’ve never been hit hard enough by a single shot (Or even a good 20 rounds) to leave a bruise… And I’m a scrawny wuss 
Just to screw up the equations even more…
Remember that in a semi-automatic weapon, some of the gases are recycled to chamber the next round. There is also large spring in them to push the bolt back the other way.
2 more thoughts…
I could see where a 12 gauge fired from under 10 feet could send a person flying.
and…
It’s always been my impression that one of the problems with the .223 was overpenetration. If it misses a bone, then it does just fly right through.
The weight of the gun has nothing to do w/ the energy of the bullet. Having to qulify w/ a weapon every year. A gun’s weight only reduces the amount of “Kick-back” that the bullet gives when fired. If you noticed when you buy ammunition at your local dealer it says that…for ex. you buy a box of .357 mag and it says that it’s a 125 grain cartidge or let’s say 158 gr. The grains are what give the bullet it’s energy. The difference of 33 grains rusult in lets say a matter of someone standing at 600 feet. 125 gr. may not reach whereas 158 gr will. As for the length of the barrel all that is for is accuracy…longer barrel…better accuracy…shorter…not so great. Recoil in rifles is softened by a rubber stopper like thing which is called a plunger.
very little energy is needed to kill you. It is not the force or the energy but how you use it and apply it.
Take a sharp, pointed, knife. I will rest the handle on my belly and the tip on your belly. Now we start pusing against each other… We obviously exert the same force but…
How much energy is needed to drive a pointed knife into someone? Not much
A bullet hurts you because it goes through you. If you have a bulletproof vest or just a flat piece of metal to prevent the bullet from going through you, it will not cause you any damage. It does not have that much energy.
Well… There’s a big difference between the kick of a gun and the impact of a bullet into a bulletproof vest. In the case of the gun, the acceleration of the bullet is much more gradual than the deceleration at the other end. So a gun gives a fairly smooth kick, while the impact of a bullet against a steel plate creates a pretty high ‘G’ pulse of energy. And that does a fair bit of damage. If you get shot while wearing one of those kevlar ballistic vests, the vest will transfer the energy of the bullet across your torso, but it’ll often leave a hell of a bruise behind. A heavier vest with steel plates has a fair bit of mass, and therefore the inertia will dampen out the impulse and make it much easier to tolerate.
If I gave you light but strong plate and had you hold it in your hand, and then shot it with a high-powered handgun, MY hand that held the gun would be fine, but I’ll bet the impact would snap your wrist, and maybe break some bones in your hand. It’s like the difference between jumping onto grass vs jumping onto concrete.
Go here for a little pertinant reading, especially some of the links.
The mass of the weapon keeps it’s velocity at a much lower level than the bullet, as JRDelirous put it. If the person firing the weapon had the identical energy applied to him as the bullet, many weapons would not be able to be fired. The .600 NE for example has a bullet muzzle energy of nearly 8000 foot pounds, with no recoil buffering as part of the weapon. With a buffer system to help absorb recoil, people are able to fire things such as the .50 BMG with over 14,000 ft/lbs or energy, or the 20mm sniper rifles with over 40,000. The shooter simply does not have the same type of forces applied to him as is applied to the bullet, due to the velocity of the weapon, the amount of distance the weapon travels during firing, and the motion of the shooter. Stand up and shoot a .600 NE and you are okay. Stand with your back against a wall and do it and you’ll get hurt.
As far as shotguns, the energy depends of course on the gauge and the load. A 12 ga., 3" shell with a 1 1/4 oz slug has a muzzle energy of about 3000 ft/lbs. This is equivalent to a 30-06, and much more than a 5.56mm. Beanbag loads do not have a great amount of energy by design. They have a lower propellant load, and a reduced muzzle velocity to prevent injury as their design is to simply stun/impart pain.
A silencer will impart more recoil, but at nearly an imperceptible level. They work by gradually reducing the gas velocity to reduce the shockwave which is what creates the noise.
Being blown off the feet when shot is possible depending on many factors such as bullet design, impact point, momentum of target, etc. Soft point and hollow point bullets increase the energy transfer much more than a solid point, against soft targets. The energy of the bullet itself is not the factor, but the absorbed energy felt by the target.
A few points: First, sound is an extremely “inefficient” form of energy. What we think of as a particularly loud sound isn’t all that significant, energetically. Heat is much more significant.
Second, the energy of the gun and bullet: Momentum must be conserved. The initial momentum of the gun+bullet system is zero, so the final momentum of the gun must be opposite the final momentum of the bullet, to cancel it out. Suppose for simplicity of calculation that the gun is .1 kilograms, the bullet is one gram, and the muzzle velocity of the bullet is 200 m/s. That gives the bullet a momentum of +0.2 kgm/s, so the gun must have a momentum of -0.2 kgm/s. At .1 kg, that means that the velocity of the gun is -2 m/s. Now let’s look at the energies: E = .5 m*v[sup]2[/sup], so the bullet has an energy of 20 Joules, but the gun has an energy of 0.2 Joules. E[sub]gun[/sub] / E[sub]bullet[/sub] = m[sub]bullet[/sub] / m[sub]gun[/sub].
By the way, I didn’t mean to imply that momentum is more significant here than energy; it’s just easier to use for the calculations. When it comes to the damage done on impact, the energy may well be more significant, but I don’t know the physics of wounds.
Sorry, but this just isn’t true. When I go target shooting with my Mini-14 (.223 cal, same as the AR-15 and M-16), One of the things I like to do is shoot at metal, just because I think it looks cool. My shots go clean through a 1/4" cast iron (not hardened steel) plate with no problem, and put a serious dent in a second plate about 1" behind. There is a huge amount of energy transferred by a bullet, depending on the caliber and distance.
A Remington 55-grain .223 FMJ (full metal jacket) round has muzzle velocity of 3,240 ft/sec. Muzzle energy is 1282 ft-lbs, or 1740 joules.
Imagine shooting a man wearing some sort of armor that will completely absorb the energy, and in full gear weighs 220 lbs, or 100kg. Since energy is MV[sup]2[/sup], and the mass of the target is 100kg (and initial velocity zero), that leaves us V[sup]2[/sup] of 17.4, or V=4.17 m/s, which is about 9.33 mph. That’s like getting hit with a 2 lb hammer moving at about 42 mph. Ouch.
My point? Bullets don’t kill ONLY by penetration. Transfer of energy is also a major factor. The bonus is that energy can be transferred directly to internal organs, since they DO penetrate. And even assuming armor that prevents penetration, there can still be significant damage. And 9mph, incidentally, is a little less than the speed of a world-record pace sprint. So depending on penetration, you could, indeed, be thrown. Not a full 9mph probably, mainly because of compression and elasticity in the target’s body, but that’s still a hell of a lot of energy to transfer.
Naturally the numbers above change drastically as the target gets farther away (v=1933 ft/sec at 300yds) and if the bullet goes all the way through (which obviously would happen at short range).
(by the way, numbers come from Remington’s website, here.
You just touched on one of the great debates of ballistics. Last I heard, nobody could prove with certainty whether it’s momentum or K.E. that kills, or which has greater effect on the severity of the wound.
But the point is well made. You can be damaged by the impulse imparted to the body by the bullet. People have been killed by bullets that didn’t hit critical organs or even penetrate the body. If you put a flak jacket on and then take a heavy caliber bullet in the chest, the rapid deceleration of the bullet will create an impulse that can feel like slamming into a wall. In some people, this can be enough to rip blood vessels in the heart and kill them. Remember how Diana died in that car accident? The rapid deceleration ripped her aorta open, even though her skin was unbroken.
When a bullet hits something heavy, the inertia of the object it hits will flatten out the impulse spike, and make it easier for a human to tolerate. For example, if you get hit while wearing a lightweight kevlar vest, it’ll hurt like hell. The kevlar fibers are incredibly strong, and might stop the bullet from penetrating. But they don’t have much mass, so the impulse from stopping the bullet is still very sharp, and can cause enough damage to send you to the hospital.
On the other hand, if you hold up a 200 lb metal plate and someone shoots it, you will probably feel the force more as a ‘push’, and you might not even feel it at all.
I may be nitpicking a little here but…
I don’t know what your track team was like, but if 9mph, or even a little more than 9mph, is a world-record pace sprint, sign me up for the olympics.
It took me a while to dig it up in my crap but here is the standard formula for calculating what the recoil energy of a weapon will be.
WB = Weight of bullet in grains
VB = Muzzle velocity of bullet in f/s
WP = Weight of powder charge in grains
WG = Weight of gun in pounds
I = Interim number (Recoil Impulse in lb/sec)
VG = Recoil velocity of gun (f/s)
EG = Recoil energy of gun (ft lb)
I = [(WB x VB) + (WP x 4000)] / 225218
VG = 32.2 x (I / WG)
EG = (WG x VG x VG) / 64.4
HAH! Duh, sorry. Somehow when I was typing, I managed to think “ok, 100m, and it’s done in 10 sec, so it must be about 9mph!”
Ok, so it’s about 1/3 of an olympic sprint. But I still wouldn’t want to be thrown that fast from my feet! 
What the detonation exerts on both objects equally is -Force- (pressure). The momentum of the weapon and the momentum of the bullet are equal in opposite directions because they are the only 2 bodies in motion in the example and the vector quantities have to add up to what they were before firing, which was set to be a state of rest.
Conservation of energy OTOH has no equal-and-opposite requirement in this case. Just as long as the system’s total energy is constant, from the chemical energy originally locked in the chemical inside the cartridge case more of it can be transformed into KE of one moving part than that of others. Also while momentum is a linear m*v function, Kinetic Energy is a function of mass and the the *square[i/] of velocity, so the very, very fast-moving round can carry a LOT more energy.
[QUOTE]
*Originally posted by Joe_Cool *
My point? Bullets don’t kill ONLY by penetration. Transfer of energy is also a major factor. The bonus is that energy can be transferred directly to internal organs, since they DO penetrate.
The bullet does nothing else other than create a hole. As we all know when you shoot a bullet the barrel puts a spin on the bullet not only to keep it from tumbling but to create 2 “air pockets” picture it. In front of the bullet there is air being broken and sent outwards…this is also happening behind the bullet but only quite larger. This is what causes the exit wound to be much bigger than the entrance wound. Yes, I know that some bullets are designed to explode on contact but still this air pockets are what causes the most damage not the bullet. But you were more or less right also
You forgot to figure the increased weight of the gun from the addition of the silencer. Hollywood notwithstanding, effective silencers are usually at least 30cm long and are relatively heavy, since they must contain the escaping gases without deforming (and thus being rendered useless for the next shot). Add in the extra weight and felt recoil will probably be reduced in most cases, assuming we’re comparing a given gun and the same gun with a 40x8cm metal tube hanging off the muzzle.
In most (semi)automatic rifles, the heavy moving part that soaks up the energy of the recoil is called, appropriately, the buffer. In the M16, that’s the thing between the rear of the bolt carrier and the recoil spring. In general, the bigger the cartridge being fired, the bigger the buffer. You oughta see the buffer in the .55 Boys Rifle (A very, very large rifle used very ineffectively against German tanks in WWII).