Katana cuts .50 cal. bullets in half - video clip

I guess it wasn't a Hattori Hanzo sword. :rolleyes:

Cool video. Sure busts some myths about swords in general and katanas in particular. It did seem to hold up pretty well against some major ordinance, all things considered.
 
This video clip come from Japanese TV proglam last year.
This katana was made by Kuzan Oda.
I saw him at the Kuzan Blade Show(Tokyo Blade Show) 2004 and heard about this.
Here is pics of his knife cut the bullet. These photographs were taken in 80's.
http://www.wildshot.net/knife.htm
 
I don't know how impressed I am. Bullets are made of lead, a very soft material.

Knives are made of steel, a very hard material.

I can cut a bullet in half with any good knife. It's just a matter of pushing hard.

Am I impressed that water, a very soft material, flows around a rock, a very hard material? No. I expect that.

A bullet fired from a gun is an object in motion. It has tremendous inertia. One definition of inertia is, "the tendency of a body in straight line motion to stay in motion in a straight line." But you have to think of a bullet not as a single object but as a collection of lead atoms. Each lead atom is an object in motion. Each atom tends to continue in straight line motion.

The atoms are held together as one lump of lead by cohesive forces. But those forces are finite.

When you try to stop a moving object, force is generated. That force is equal to mass time deceleration. Bullets have considerable mass, 250 grains maybe?, and a bullet may be traveling perhaps two thousand feet per second. To change it's velocity from 2000 FPS to zero over virtually no distance (assuming the knife does not move) is a huge deceleration. Multiply that by a considerable mass and you have huge force. That force is what makes a bullet a viable weapon. Any attempt to decelerate a bullet in flight results in a huge force.

The edge of a knife is very, very thin. So, let's go back to thinking of the bullet not as a single object but as a collection of atoms held together by a cohesive force. If the bullet were to hit, for example, a wall (assuming bullet-proof), all of the atoms would be stopped at the same time. But when the bullet hits a knife edge, only a small fraction of the atoms are directly stopped.

The question now becomes: which is greater, the cohesive force holding the "non-blocked" atoms to the "blocked" atoms, or the inertia of the non-blocked atoms?

The analogy that can be used is a line of people each holding the hand of the person on each side and all marching forward together in lock-step. Each person is an individual, but they are held together. What happens if this wide line of people encounters a post sticking up out of the ground? If one person happens to encounter the post, he will be stopped. But the people on each side of him will go on. Eventually, he will loose his grip and the line will be broken. But, the two parts of the line will move on.

Has anyone ever done this experiment with other knives?
 
That was great!
I love the way they drag the American in for his "Big American Machine Gun!"
 
When a bullet is thusly cut, as I said, a considerable amount of energy is involved. Some of that energy is dissipated in the form of heat. Specifically, it heats the blade. Heating steel has the effect of hardening it. As a result, each time a bullet is cut, the blade becomes harder and harder in that area. A hard blade is a brittle blade. So, that will contribute to the eventual failure of the blade.

It would have been interesting to have done Rockwell tests on the blade or even taken x-ray crystalgraphs of it before and after to measure local hardening.
 
SOG has a similar picture somewhere on their website. I believe it was a seal pup that cut a bullet in half. some procedure, and given the speed of the bullet, nothing special in my eye.

I believe that if you'd hit a razorblade straight with a bullet like that, it would cut it in two pieces as well.
 
I love the way they drag the American in for his "Big American Machine Gun!"
Click to expand...

Yeah, and he's gotta be a big American.

The thing I liked was the flying to America to do the experiment. Apparently, this sort of thing can't be done in Japan.

I liked the guy carefully cleaning the sword blade off before the test... as if that's gonna make any difference.
 
Gollnick said:
Has anyone ever done this experiment with other knives?
Click to expand...
Here's a pic of a .45 bullet split by a SOG, I remember seeing this years ago in one of their catalogs.

(Edit: Fiddlesticks! Richard beat me to the punch.)

sogshot.jpg
 
It's interesting to note, that the bullet in SOG's photo is "jacketed." The bullets being used in the Japaneese vide also appeared Jacketed. Most bullets are. A jacketed bullet has a thin coating of some other metal (usually copper) over the lead. The jacket is necessary because the energy imparted to the bullet by the explosion inside the gun will create forces greater than the cohesive force holding the lead atoms together and the bullet will literally disintegrate. The jacket holds the lead atoms together. What that demonstrates is that the cohesive forces holding lead atoms together aren't that great.
 
I can't help but think that there is a lot of difference between a 230 grain bullet moving at 900 fps and a 700 g bullet moving at 2800 fps. Anything that can stand up to a single hit by a .50 bmg has my respect, much less multiple hits.
 
Gollnick said:
Bullets have considerable mass, 250 grains maybe?, and a bullet may be traveling perhaps two thousand feet per second. To change it's velocity from 2000 FPS to zero over virtually no distance (assuming the knife does not move) is a huge deceleration. QUOTE]

Actually a M-2 50cal bullet is closer to 700grains and traveling over 3000FPS.
Click to expand...
 
I don't have the link but I saw the video of the water jet cutting a deba or kitchen knife in half longitudinally (the image of it wasn't real clear in this video but it basically made 2 knives out of one), so it was interesting that the ninto survived that unscathed. I'm not impressed that it can split soft lead pistol bullets.

However, I am surprised that the sword held up as well as it did to the machine gun fire, needing several rounds to chip away at the blade.

50 cal ball ammo is a steel core tipped with lead-antimony and encased in gilding metal (copper 95% zinc 5%). Armor piercing have a tungsten core and can penetrate an inch of armor plate at 200 meters, but we'll assume standard ball ammo which can only do the same feat at the closer range of 35 meters:
Projectile Mass: 42.12 g (650 gr)
Muzzle Velocity: 887.0 m/sec (2910 fps), @ 23.8 m (78 ft) from muzzle
Muzzle Energy: 16,569.5 Joules (12,221 ft.lbs), @ 23.8 m (78 ft).

With a steel core bullet delivering that kind of energy, I'm amazed that it took so many shots to actually break the blade, considering that once the sharp, hard edge was chipped, the blade integrity was spoiled and succeeding rounds could do more and more damage.

Oh, for those of you who hate noisy neighbors waking you up with their lawnmowers on Saturday morning, here's a couple of other videos.

http://www.serbu.com/lawnmwr.htm

If the link is down here is an alternate site
75 round clip AK47 fired at a lawnmower http://tlf.cx/ak47.mpg
50 cal incendiary round at same mower http://tlf.cx/cal50.mpg
 
Actually a M-2 50cal bullet is closer to 700grains and traveling over 3000FPS
Click to expand...

Even greater force, then.

F=MA where F is force, M is mass, and A is the absolute value of acceleration. Deceleration, when something stops, is just negative acceleration, but the equation for force uses the absolute value of acceleration, so that distinction doesn't matter.

Acceleration is change in velocity over distance, A=dV/dX. When a moving object hits an immovable object, the distance, X, becomes vanishingly small. If dV, the change in velocity, is very high, going from 3000 FPS to zero, for example, well a very big number divided by a very small number equals a huge number. Acceleration becomes huge.

F=MA. If acceleration is huge, then unless mass M, is very small, force F is going to be huge too. And 250 grains much less 700 is actually a fairly large mass.

That force can very easily exceed the cohesive force that holds atoms together. This is how a bullet can penetrate a piece of steel.

But, when that force is applied to only a very small part of the bullet and the bullet is made of lead which has very low cohesive forces, it's not surprising that the force of inertia exceeds the cohesive force and the bullet is cut in two.
 
Gollnick said:
I liked the guy carefully cleaning the sword blade off before the test... as if that's gonna make any difference.
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tongue-in-cheek, right? :confused:

cos there's a lot more than beating steel or iron to shape in swordmaking, especially in creating a nihonto. reverence, pride, culture, ceremony etc...
 
I don't think this video illustrated or attempted to illustrate a point that a Katanna would stop a .50 Caliber BMG round by cutting it in half. In fact, I believe it was done, merely to show that it was possible. Never the less, I for one am impressed that it took I believe it said 7 rounds fo .50BMG to finally break the Katanna. Sure, it's not that amazing it cut the round in half, the same could've happened if it hit any thin hard surface, but the fact that it took multiple rounds to destroy the blade IS impressive.

-Rob
 
How do we know that the bullets were travelling at mil-spec speed?
They could have been downloaded to a level that was just high enough to cycle the action.
 
spyken said:
tongue-in-cheek, right? :confused:

cos there's a lot more than beating steel or iron to shape in swordmaking, especially in creating a nihonto. reverence, pride, culture, ceremony etc...
Click to expand...

So "pride", "ceremony" and cleaning it before shooting at it with a heavy machine gun are going to make a katana blade perform better?
 
This is what's called a culture barrier. It's not about making it perform better, it's out of respect for what it is, and how such blades are meant to be treated. I'm quite frankly surprised that they put this whole thing together, since I'm pretty sure they knew the blade would be destroyed with the .50 BMG. Anyways, even though I have no idea how other blades might hold up, 7 rounds to snap the blade in half seems really impressive. After the first shot you could see the edge chip/impact. I figured the 2nd shot would have been the one to break it, not the 7th.
 
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