In the newest Rambo film Rambo sets up a simple trap but putting a bunch of bullets in metal tubes (looked like 7.62 or 5.56) and burying them so that the bullet tip just barely pokes out of the ground. The implication of this is that somebody steps on the bullet and presumably there’s something hard underneath the bullet to trigger the primer causing the bullet to immediately shoot upwards into whoever stepped on it.
I always heard that bullets without the aid of a barrel to guide them nor enough velocity to build up behind them would simply pop like fire crackers and not be able to penetrate anything. Anyone know if this is the case?
Mythbusters tried it, and they found exactly that. A bullet relies on the pressure from the exploding gunpowder behind it to accelerate down the barrel. With no barrel to contain the pressure and direct it all towards the target a bullet isn’t going to do much.
The bullet won’t fly far if detonated outside of a gun, but if you step on it, you are constraining the explosion with your foot, and you will have a very bad day.
If you take a .45 Colt handgun with a blank round in it and put the barrel an inch away from a piece of 1/2" plywood, the blast and paper wadding alone will blow a hole though the plywood. I know, because I’ve done it. Jon-Erik Hexum killed himself accidentally that way, putting a gun loaded with blanks up to his head on a TV set and pulling the trigger for fun. The blast fractured his skull and drove the paper wadding into his brain.
I don’t know how easy it would be to set off a shotgun shell by stepping on it with a nail on the primer, but if you do, your foot and leg are going to get messed up.
I think the replies so far might have neglected an important detail in the OP. See the bolded bit:
If there are metal tubes involved that aren’t connecting the bullet to the powder to the primer, you’ve basically got a barrel.
The case could rupture and vent some of the gas, sure. Or maybe your tubes are made from pot metal and they rupture. And with bottlenecked cases, plenty of gas would leak past the bullet. But even if we’re talking a 5.56-mm bullet moving at 600 feet per second, I’ll step around, thankyouverymuch.
Did Mythbusters use metal tubes? If so, why didn’t they work on the show?
I’d expect a non-bottlenecked round (like a 9-mm) in a close-fitting pseudo-muzzle tube to have a pseudo-muzzle velocity on the order of that of a snubnose revolver. But maybe I’m way off base.
You don’t need a seal. The explosion releases a bunch of energy. The ground will absorb some, and so will your foot.
If you held a shotgun shell without bb’s tight in your fist with the opening pressed into your palm and set it off, what do you think would happen to your hand?
That’s a good description of the feeling. I was 10 at the time.
I was unloading 9mm ammo with an impact hammer once. An impact hammer is a T-shaped hammer with a hollow plastic head. You load the cartridge at one end, facing the other end, and you slam the side without the cartridge in it on a hard surface. Inertia causes the bullet to slip out of the casing, and you then have an unloaded case.
Well, I was having a bad day, wasn’t paying attention, and I slammed the cartridge side of the hammer on the table. It went off. It blew the opposite end of the hammer off, the casing ruptured, and interestingly there was unburned powder everywhere so you know you’re not getting full velocity out of the bullet as it’s incomplete ignition. Still really loud though.
American Rifleman did a study years back on how dangerous ammo in fires were to firemen. They did a number of tests using various rifle and pistol caliber cartridges placed in a holder and exposed it to flame (each caliber one at a time, not all at once). Next to it was a fireman’s bunker coat. When they went off neither the bullet or copper case fragments penetrated the coat.
I don’t agree with your thinking here. I’m basing my thinking on the OP’s description in which there is a metal tube but the metal tube is shorter than the tube, so the bullet sticks out of the ground. Is that really how the trap in the movie worked?
If so, the tube isn’t really acting as a barrel. The tube might help the base of the cartridge from rupturing under pressure but it does nothing to keep the case neck from rupturing or expanding to the tube diameter. Lots of gas is going to escape from there. I also don’t think it’s much like shooting from a snub-nose pistol. The pistol offers a couple of inches of barrel after the bullet has left the cartridge to allow the gas pressure to continue accelerating the bullet. With our Hollywood bullet trap, the pressure only builds behind the bullet for as long as either (1) the case hasn’t ruptured or expanded at the top, or (2) the bullet leaves the cartridge. I don’t feel like looking up bullet seating specs for these cartridges, but the bullet is only going to be seated a few millimeters into either. That means the bullet has only a few millimeters at best to accelerate before the gas leaks away. I think the bullet velocity differential between a snub-nose and this bullet trap would be comparable to the difference in velocity of a dragster at 60’ versus a 1/4 mile.
That’s a fair point—in the scenario described by the OP, a tube-based pseudo-barrel would have to be 2-3 mm shorter than the bullet itself, so my comparison to a snub-nosed revolver doesn’t hold water.
Even so, the tube ensures that the bulk of the blast energy is directed into the victim’s foot, and the effect from an aural-only “pop” to a gorier one. In Sam Smith’s example, a blank—with less powder than a regular cartridge—penetrated that poor guy’s skull. Stepping on a 7.62-mm rifle cartridge in a tube would likely ruin your whole day, even if you’re wearing steel-shank boots.
If you’re using a rimmed cartridge like a .357 magnum, the tube/barrel could be arbitrarily long—the bottom rim of the buried tube would engage the cartridge rim, driving it into the firing pin/nail. That would be like firing a .357 magnum into the sole of your foot. But I admit that’s considerably more elaborate than what the OP saw in the movie.
One is, well, exploding; the other is burning fiercely. Modern propellants and even black powder don’t really explode unless they’re confined – think of an old-fashioned powder train. A block of C4 will explode whether it’s confined or not.
What if you had a tube a couple of inches long with several bullet stacked in it? Only the tip of the top bullet pokes out of the tube, but stepping on it fires the bullet at the bottom?
Agreed. If the cartridge goes off under foot pressure, then I think it would likely injure the stepper’s foot pretty badly. I just didn’t think the tube, as described by the OP, really added any velocity.
So can anyone confirm that the pressure from a relatively normal footstep (as opposed to a hammer blow) would set off the primer? That’s the real reason I question whether this trap would work. Darren Garrison’s cites say it works but they aren’t the strongest cites. One is essentially asking for verification of an internet rumor. The wikipedia entry is backed by a real book but that’s just one source.
Pet peeve: A bullet is the projectile. In order for a bullet to be projected, it must be put into a case with a primer = cartridge. Even with any gunpowder, the primer alone may have enough force to “fire” the bullet.
Pet peeve: No Hollywood movie would show the full/accurate process of making a lethal device.
Which leads to the crucial missing element. The primer requires a significant amount of pinpoint force in order to fire. Just the force of stepping down on the bullet, forcing the cartridge down upon the improvised firing pin is unlikely to cause the primer to work. In the forum Darren Garrison linked to, it’s explained that a spring loaded “firing pin” is required to provide enough force to cause the primer to ignite.
It seems instantaneous, but as Ike Witt states the gunpower deflagrates (had to look it up*), i.e. ignites/burns from the bottom up, not nearly all at once, which would be a detonation. Without a barrel, there’s not enough time for all the gunpower to ignite**, reducing the speed/force of the bullet. It will still be traveling at high speed, though far less lethal than one from a barrel/tube.
*“Deflagration (Lat: de + flagrare, “to burn down”) is subsonic combustion propagating through heat transfer; hot burning material heats the next layer of cold material and ignites it. Most “fires” found in daily life, from flames to explosions such as that of black powder, are deflagrations. This differs from detonation, which propagates supersonically through shock waves, decomposing a substance extremely quickly.”
**This is happened to Patch. There wasn’t enough time for all the gunpower to ignite inside the case. In barrels too short to allow all the gunpower to ignite in the barrel, some of the gunpower may be forced unburned out the barrel. In this video https://www.youtube.com/watch?v=QSlLZeWLy3s, start at 0:56, notice that the bullet is followed by gas (the ignited gunpower), then by glowing particles (the gunpower ignited outside the barrel), then dark particles (the unburned gunpower).
Adding onto that, the reaction rate for burning smokeless powder is directly proportional to the ambient pressure. Burn powder in the open, it burns nicely, but it wouldn’t be mistaken for an explosion. Confine the reaction, like in a cartridge case placed within a vessel that did not allow for much expansion, like a firearm’s chamber, and the reaction proceeds a LOT faster.
AIUI—and if someone like Tripler wants to correct me, great—once initiated, explosives’ reaction rates don’t depend on their confinement. Explosives are buried so that more of their released energy may perform work on the desired workpiece, and not wasted to the air or to flyrock. But their detonation velocity is much the same if detonated in open air vs confined in say a borehole.
One does not use Spitzer bullets in cartridges meant for use in tube magazine rifles because the force of recoil can be enough to cause the pointy bullet of one cartridge to set of the primer of the cartridge in front of it. Chain reactions involving the other cartridges are possible. The results are unpleasant for the shooter.
