'Shotguns have dkb/dbt' - where did that myth (?) come from?

[vicky_molokh]

Greetings, all!

Several times in my life I've encountered the opinion that shotgun attacks have so much 'push' that despite not penetrating the armour (vest or whatever), the blast is enough to break ribs, cause internal bleeding etc. I've even heard of an 'advanced' bulletproof vest which was made not only hard but heavy specifically to resist this 'shock'. I think this is wrong, judging by many posts of the local guns experts, but of course I could've misinterpreted them.

So it's a myth, right? Where did it come from, especially the 'shot-proof vest'?

Thanks in advance!

[Mailanka]

Movies.

You can really see this, for example, in Hard Boiled.

[Jerron]

Any firearm has the potential for that sort of thing. Shotguns just tend to pack more energy into the whole, personally I think a lot of it is wasted with pellet dispersal, or something.

Anything that completely stops the projectile(s) will absorb that energy. Pistol rounds into a bullet proof vest will do it as well, there's just a lot less energy to start with. (All you guys with the slide rules, calm down. All I'm saying is there's a lot more propellant in a 12g shell than a 9mm cartridge.)

I guess there are two factors:
1) How flexible the armor is. I've worn Vietnam-era flak jackets, and trust me, nothing that you will survive is likely to do blunt trauma through it.
2) How powerful the round is. A .50 Browning round is gonna hurt through even semi-flexible armor. In fact, that one might actually hurt through a half inch of solid steel, because if you aren't using the armor piercing (which will go through that like a hot knife through butter) it *will* bend the steel, making it semi-flexible, at least for that round. A 9mm barely hurts through clothes (my opinion- it definitely makes a hole, I'm just saying the contusions from non-penetrating wounds is way low compared to the bloody part).

I've had .38's, almost the same as 9mm but a bit more powerful, actually bounce off of plywood. From the same range, a shotgun will rip a hole the size of a baseball or softball (depending on other factors). Bottom line is, with enough energy, any round will do what you're saying. Shotguns are just the most likely culprit, because handguns are wimpy compared to long guns, and people tend to use shotguns much more than high (super?) powered rifles. (Note I'm talking something above normal military calibers, perhaps sniper size for long ranges. Normal hunting rounds would likely be a little less energy than shotguns, but that energy would be delivered at about the same amount at a much greater range.) Range is also a factor, if you've ever looked at the way bullet resistant vests are rated, they mention it was tested and able to stop X caliber at Y distance. So while they say 'able to stop a shotgun', it's more a measure of overall performance, with shotgun being at the top of the list of likely threats. I have never seen one say 'able to stop high-powered rifles', because when you start getting into the high end of the performance there, you can get into some hugely powerful stuff that you can't stop without boiler plate. (Like the .50 armor piercing where even 1" of solid steel just won't work.)

[lwcamp]

Originally Posted by Molokh

Several times in my life I've encountered the opinion that shotgun attacks have so much 'push' that despite not penetrating the armour (vest or whatever), the blast is enough to break ribs, cause internal bleeding etc. I've even heard of an 'advanced' bulletproof vest which was made not only hard but heavy specifically to resist this 'shock'. I think this is wrong, judging by many posts of the local guns experts, but of course I could've misinterpreted them.

So it's a myth, right? Where did it come from, especially the 'shot-proof vest'?

A 28 gram shotgun slug striking at 500 m/s will have 3,500 J of kinetic energy and 14 N-s of momentum.

The 7 kg arm of a karate master punching at 7 m/s will have 170 J of kinetic energy and 49 N-s of momentum. Top karate experts can go a bit faster, up to 10 to 15 m/s, for a maximum of perhaps 100 N-s and 700 J of kinetic energy. A boxing champion (Rocky Marciano) once has the energy of his punch measured at 1250 J using a ballistic pendulum.

Very roughly, momentum is what pushes things around, and energy is what stretches, tears, and breaks things. A punch will push someone around more than a shotgun slug, but even if stopped by a ballistic vest, the energy of the impact will still be able to break things much better than a punch - by about an order of magnitude. It is estimated that a leg bone takes about 350 J to break, an arm bone about 90 J, and a rib bone perhaps 30 J. So a strike by a shotgun slug stopped by a ballistic vest can still smash plenty of ribs.

That is assuming that the energy is efficiently transferred from the slug to the ribs. Trauma plates can distribute the energy over a wider area, and padding and stretchy Kevlar fibers can use up some of that energy before it gets to the torso. I suspect you are still looking at bruising and cracked ribs, though, even if your chest isn't caved in.

However, the paucity of momentum compared to a punch means that a shotgun slug will not be particularly good at knocking people over. They might, however, drop to the ground from pain after getting their ribs smashed up.

Luke

[Anthony]

Originally Posted by lwcamp

The 7 kg arm of a karate master punching at 7 m/s will have 170 J of kinetic energy and 49 N-s of momentum.

Um...wow. 7 kilogram arms? I think you're vastly overestimating the weight of the arm, particularly the amount of the arm which is actually moving at peak speed; based on how much water I displace when I put my arm in a container of water, the forearm is maybe 1 kilogram. For reference, knife-proof vests are generally normalized for a 40J impact, which is more than most people can actually deliver.

Of course, knocking someone back with a punch also pretty much doesn't happen, unless they fall over from the shock. About the only impacts which realistically cause any level of knockback are collisions or other similar attacks which involve the full body weight behind the blow.

[vicky_molokh]

Originally Posted by Anthony

Um...wow. 7 kilogram arms? I think you're vastly overestimating the weight of the arm, particularly the amount of the arm which is actually moving at peak speed; based on how much water I displace when I put my arm in a container of water, the forearm is maybe 1 kilogram. For reference, knife-proof vests are generally normalized for a 40J impact, which is more than most people can actually deliver.

Of course, knocking someone back with a punch also pretty much doesn't happen, unless they fall over from the shock. About the only impacts which realistically cause any level of knockback are collisions or other similar attacks which involve the full body weight behind the blow.

My biomech is pretty rusty, but IIRC the torso is 40% and arms are 9% the weight of the human normally.

I'm also surprised that a punch of a respectable combatant is less than 10m×s^-1.

[Anthony]

Originally Posted by Molokh

My biomech is pretty rusty, but IIRC the torso is 40% and arms are 9% the weight of the human normally.

Depends on what you count as being the arms, but in any case, that would give 7 kilograms for both arms put together, and at that weight probably includes upper arms and shoulder, which aren't really part of the impact mass of a punch.

[Langy]

A well-delivered punch shouldn't just use the mass of the arm, should it? I'd think a power punch would involve putting the torso behind the blow rather than just the arm - or at the very least, the shoulder.

Then again, I haven't practiced any martial arts in over thirteen years and the only time I punched anything since then I broke one of my fingers, so I'm not exactly an expert.

[vicky_molokh]

Originally Posted by Anthony

Depends on what you count as being the arms, but in any case, that would give 7 kilograms for both arms put together, and at that weight probably includes upper arms and shoulder, which aren't really part of the impact mass of a punch.

Yes and no. An arm by itself is (for simplicity, if not anything else) considered as the part which moves when the torso is fixed, i.e. everything from the shoulderjoint. But the thing is, a punch doesn't involve just the arm moving. It involves the torso turning, a large aid from the hips, and (assuming something like [url=http://www.youtube.com/watch?v=WcsqA4ncnzYoi-zuki[/url] [watch near the very end]) a long step forward.

[Anthony]

Originally Posted by Langy

A well-delivered punch shouldn't just use the mass of the arm, should it? I'd think a power punch would involve putting the torso behind the blow rather than just the arm - or at the very least, the shoulder.

A well-delivered punch involves torso muscles, but the actual impact mass is much smaller. Essentially, a punch uses a mechanism very similar to a whip crack to transfer rotational energy generated in the hips and torso into hand velocity, but the mass which is actually relevant for knockback purposes is only the hand and for some types of strike the forearm.