Can bullets knock people down?

Read this FBI report saying this whole “stopping power” and “knock-down ability” in large caliber handguns was a myth. There was also an episode in Mythbusters supporting this. But I have a couple of mouthfuls to say to both:

  1. It’s not true that a human cannot launch a bullet at 1,000 foot-pounds of energy (.44 mag) from the hand. Of course you can. It’s not like you’re shooting yourself at the same time with a similar bullet.

  2. A “knock-down” shot should also knock down the shooter. WHAT? The firearm is heavier and shaped differently from the bullet. You have several points wherein “sticky” collisions occur (the gun’s recoil, the hand and arm’s flexing, shoulder and body muscles slightly yielding.) Body mechanics will direct the remaining recoil energy down one’s rear leg into the ground.

  3. A bullet hitting a human is likewise a sticky collision and not all of the bullet’s kinetic energy will be transferred into the body. But you have instances wherein something like that can really happen.

So why can’t a .45 auto (500 f-lb) knock down a man? In Mythbusters, you have a man with his feet braced firmly on the ground, holding a bullet-proof shield to his body. The 500f-lb shot didn’t knock him down. Well, that was a practiced move. A healthy man can brace himself against the ground strongly enough to push a car uphill. But the same man can be knocked down by a strong slap (50 f-lbs.) or a .22 bullet if he’s not prepared.

Energy doesn’t knock things over, momentum does. And the shooter gets exactly as much momentum from a bullet as the target does. It really is as simple as that.

Mythbusters also fired a bunch of different rounds at a very-precariously-suspended pig carcass, and only one (shotgun blast) so much as nudged the pig the necessary few inches for it to slip its leash and fall straight down. No getting knocked back through a plate glass window. Isaac Newton. What a kidder.

Well if we want to be pedantic the shooter gets more momentum than the target because he gets the momentum of the bullet and the expanding gasses which don’t make it all the way to the target. Also the bullet dumps some of its momentum into the air as it travels through it, reducing the amount of momentum the target gets even more. (But I’m taking a guess when you sum it up the difference wouldn’t be that much.)

If he doesn’t watch it, he’s gonna get blown off the shoulders of those giants through a plate glass window.:wink:

Mythbusters used this principle to test shooting a gun out of someone’s hand. Since none of those wimps was willing to hold a gun while someone else shot at it, they set up a gun that shot out the side instead of the front.

Since people can be knocked over from shooting a gun (though usually because they are not in a good stance I think), then you must be able to get knock someone down with a gunshot.

I would imagine that the reason people get knocked over after being struck by a bullet has to do more with shock and pain than due to momentum.

No. Wrong. Completely. Fall down, yes. Knocked down, no. Not unless he was standing on tip-toe on a narrow beam that was revolving during an earthquake.

I’d think that too. But it shouldn’t require too much momentum to knock someone over if they haven’t braced themself in the direction the bullet is traveling. It’s probably quite easy to know someone over by shooting them in the back, even if their back was armored.

A shooter is braced and using a firearm designed to deliver the force in a way he can easily absorb it, while the person being shot can be in any position. But it turns out the momentum transfer is a lot lower than you’d think, something less than half a meter per second I think. It might knock over a person if it hits them at the right angle, but not a solid shot on a standing person with both feet on the ground. Here and here are people with bulletproof vests voluntarily being shot without being knocked down, or even visibly moved really.

You’re confusing two different issues. “Stopping power” refers to stopping the threat. This occurs when a bad guy is injured badly enough to make him unable to continue the course of action that got him shot. He may be still on his feet, but he’s no longer a threat.

People falling down when they get shot comes from other things. A part, such as a knee with body weight on it, that is vital to standing, may be shot. A person may fall simply because the body part is no longer able to support the weight.

However, a second cause of falling, and quite possibly the bigger cause, is simply the result of people thinking that they’re SUPPOSED TO FALL. After all, that’s what the movies show. In other words, people fall when shot because they’ve been conditioned to fall when shot.

In real life, however, when a person is not so conditioned, even a fatal wound is not necessarily immediately incapacitating.

I think the elephant in the room is that while a bullet may have some absurd number of foot-pounds, the total energy is still in the ballpark of being hit by a hard thrown baseball or something like that, which won’t generally knock you down unless you’re off balance, not expecting it, etc…

What makes that bullet lethal and that baseball not lethal is the size and density of the projectiles- the bullet is small and dense, and the baseball less so, so the bullet pokes a hole in you, and the baseball bounces off.

It’s more likely that the baseball would knock you down- it’s not spending its time penetrating your body like a bullet would be, so more of the energy is spent on impact to you, not in penetrating you.

Look at this way: if bullets could knock you down, magicians wouldn’t be able to catch them in their teeth! :slight_smile:

Seriously though, bullets are just too small and travel too fast to knock people or almost anything else backwards.

Over the years I’ve seen lots of videos of people being shot. Some got shot by cops (multiple times on occasion), some were shot while storming the beach at Normandy in WWII, and some were machine gunned by Nazis while standing in large ditches that were to become their grave. In none of these cases did the body of the person shot react as if it had received a blow. Mostly they just crumpled, though some of the soldiers pitched forward due to their own momentum. But again, their bodies gave no visible sign of having been shot. If you didn’t know better, you’d think they just crumpled to the ground for no reason.

Recall also John Connelly being hit by the bullet that went through Kennedy’s neck. He suffered a through-and-through wound to his shoulder/upper chest and gave no visible sign other than to yelp in pain and turn back to see what had happened.

I think most people’s impressions are conditioned by what they’ve seen in the movies, in which getting shot often sends people flying backwards (perhaps off/out a dramatically located ledge/window/etc).

TV tropes article on this subject:

(Discusses both why we think it should happen and why it doesn’t)

Others have addressed this already, but anyway:

The size, shape and mass of the firearm is largely irrelevant - it means the gun stock doesn’t penetrate your body, but the transaction of energy imparted to the system of stuff that comes out of the barrel (bullet, gases and particulates) must equal that imparted to the system of gun+shooter. Newton is quite insistent.

Yes, the shooter is in a prepared stance and the target is not, but if the bullet was capable of lifting a person off their feet and throwing them several yards through a window or against a wall, the equivalent force to the shooter would be too great to be dissipated by careful positioning.
I’m not even sure what you mean by ‘sticky’ collisions. Inelastic collisions mean the force is transmitted effectively (whereas elastic collisions would leave the shooter standing, but the gun would go bouncing off forwards).

(bolding mine)

I don’t know if you’re referring to the former (muzzle blast momentum) or the latter (bullet momentum loss due to air resistance), but the momentum from the gunpowder gases is quite significant, at least for a rifle round. You can experience this quite easily by shooting a rifle with and without silencer. With a normal high-powered rifle round like a .223R or a .308W, a silencer will effectively cut the recoil by some 50% since the gases will exit the muzzle at relatively low velocities impacting only a negligible momentum to the gun.

Just to reiterate, everyone: The knocking-down effect (or lack thereof) is due to momentum, not energy. There’s no law that says that the shooter and the target must receive the same energy, and in fact they don’t. Which is quite fortunate, since the damage done is mostly dependent on the energy, and you want the damage to be at the target, not at you.

Can a bullet knock you off balance? I suppose it could. But if you shoot a 100 pound pig carcass, it doesn’t fly backward several feet, or even several inches. It just sits there. If the pig was still alive it might lose its footing and fall down. But that’s not because it was hit by a blow that knocked it back several feet/inches.

Even if you’re shot by a 50 caliber BMG you don’t fly backwards. Your body just gets shredded. Remember that every joule of energy that goes into shredding tissue is a joule of energy that isn’t going to knock the target backward.

A tiny little tap might cause someone to lose their balance and fall down if they aren’t balanced right. Human beings are constantly adjusting their balance and any interference in the process can cause them to fall over. But the person falling might just as well fall to the side, or towards the path of the bullet, rather than away. People are sometimes knocked over when they fire guns, so it’s pretty easy to imagine that someone might lose their balance when they get shot. But that’s not the same thing as being blown backwards by several inches. Like I said, shoot a pig carcass with a variety of ammunition, and see if it is knocked backwards by several inches.

As noted above with the baseball example, an elastic collision (one where the projectile bounces off of you) would do a lot more to cause you to fly backwards than an inelastic collision (where the projectile merges with you). The best way to make a projectile that would cause a person to fly backwards would be something that bounces off of them backwards, and doesn’t compress easily. Say, oh, a jetstream of pressurized water. (See riot police)