Blast Lung Injury and Obscenely High Muzzle Velocity

[Wyrm]

The following scenario came up when I was writing some SF: A biowank baddie confronts a hero armed with exotic weaponry and armored with exotic armor. After the biowanker boasts, the hero takes out his Handgun of Doom and shoots the biowanker with a 50 cal round with a muzzle velocity of some obscene Mach number, and turns the biowanker's head to a fine red mist.

In the description of the sonic boom produced by this weapon's bullet is that it would turn an unarmored man's lungs into liquid at twenty paces. Basically, this is blast lung injury (BLI) severe enough to put a guy six feet under, period. (Please note that the hero is protected by his exotic armor from these nasty effects.)

So this leads me to a series of questions, which will lead to the minimum mach number of this weapon.

* How hard does a man's thorax have to be thumped to liquify his lungs? (And how do we measure "hardness of thump" here anyway. I suspect it's some combo of pressure and displacement.)

* From this, how does a sonic boom dissipate as it propagages? I suspect that for the front and back, it is an inverse-square law, but for along the path of the bullet, pressure would be proportional to 1/r, due to the fact that the dissipation is cylendrically symmetric, and the problem becomes 2-dimensional — help is very appreciated here.

* How strong a sonic boom does the bullet generate at its surface for a given mach number? I strongly suspect that it's related to the amount of air plowed out by the bullet as it shoves aside air as it travels. However, I expect there to be complications: for instance, how large is the displacement region about the bullet, which will effect the pressure change of the sonic boom.

With this, I can come up with a mach number for this Handgun of Doom, and be able to compute any blast effect fun in the future.

Thanks for your time. I will, of course, give credit to this thread for any information forthcoming!

[Napoleon the Clown]

Well, for it to be lethal, an explosion need only generate about five pounds of overpressure. A stick of dynamite can pull this off, especially if the stick goes off within arm's reach.

So, for the sonic boom to be lethal in and of itself, it would need to displace as much material in a short amount of time as a stick of dynamite would. I don't know what rate dynamite does this at (mebbe a resident explosives nut could help?), but it's going to be rather impressive. Now, to figure out the velocity of the round, we need to know the shape of the tip (is it rounded? pointed? concave?), how long the tip is, and if the round has any oddities that'd increase drag (and thus decrease the velocity needed to displace a certain volume of air in a certain timeframe.).

Other factors that would determine more exact velocities would be air temperature, humidity, and elevation. Keep in mind that, when shooting into water, the force of the water getting displaced can be lethal in and of itself. Ever watch Mythbuysters? The episode where they shoot a 12 gauge slug into the tank of water demonstrates this effect nicely, and they address the issue even more directly in the "Shooting Fish in a Barrel" episode.


A guess, though, would put the muzzle velocity at in excess of escape velocity. And the recoil would probably end up at unmanageable levels. The round would potentially vaporize near instantly from friction, too.

Which makes me ask... WHY? Why in hell would someone make a gun like that? What are they going to power it with?

[Darth Wong]

You would need welding goggles to fire an extreme hypersonic projectile weapon, because the air shock would create luminescent plasma. It would be just like looking directly at an arc welder. Without protection, it would blind you.

[Wyrm]

Well, for it to be lethal, an explosion need only generate about five pounds of overpressure.

I assume you mean five pounds per square inch (psi) of overpressure. Pounds, of course, being force and not pressure.

5 psi overpressure translates to ~34.47 kP overpressure.

A stick of dynamite can pull this off, especially if the stick goes off within arm's reach.

I figure the mass of a stick of dynamite to have a volume 98.17 cm³ and initial density of 1.8625 g/cm³ as it goes kablooie. The mass of the nitroglycerin (I assume you're talking about a nitro-dynamite here) works out to 117.80 g.

So this charge produces 5 psi at about 3 feet... Hmmm...

So, for the sonic boom to be lethal in and of itself, it would need to displace as much material in a short amount of time as a stick of dynamite would. I don't know what rate dynamite does this at (mebbe a resident explosives nut could help?), but it's going to be rather impressive. Now, to figure out the velocity of the round, we need to know the shape of the tip (is it rounded? pointed? concave?), how long the tip is, and if the round has any oddities that'd increase drag (and thus decrease the velocity needed to displace a certain volume of air in a certain timeframe.).

The round has a cowling on it to let it slip through the air.

Other factors that would determine more exact velocities would be air temperature, humidity, and elevation. Keep in mind that, when shooting into water, the force of the water getting displaced can be lethal in and of itself. Ever watch Mythbuysters? The episode where they shoot a 12 gauge slug into the tank of water demonstrates this effect nicely, and they address the issue even more directly in the "Shooting Fish in a Barrel" episode.

Um, yeah. I do know that.

A guess, though, would put the muzzle velocity at in excess of escape velocity. And the recoil would probably end up at unmanageable levels. The round would potentially vaporize near instantly from friction, too.

I did say this was an exotic weapon coupled with an exotic armor. The materials and construction of both are up to the task... whatever that task may be.

Which makes me ask... WHY? Why in hell would someone make a gun like that? What are they going to power it with?

To fight biowank. There's something to the biowank here — and since it's really a fanfiction, I have to play this level of biowank as I judge it. This guy has the tools and talent to spank this particular biowank hard.

Maybe the gun's power needs some calibration...

You would need welding goggles to fire an extreme hypersonic projectile weapon, because the air shock would create luminescent plasma. It would be just like looking directly at an arc welder. Without protection, it would blind you.

Ah, of course it would. I should've realized this. I take it this charming effect comes into play when the work done on the gas to compress it to the sonic boom pressure heats it to incandescence. Am I right?