"Matrix" special effect: bullets spinning toward Neo (spoiler)

SPOILER BELOW
A couple days ago, I rewatched “Matrix” and became transfixed by the wild climax at the end, when Neo slows, then stops, the handgun bullets midflight.

Although I know a bit about the rifling of bullets, I guess what I’m wondering is if the tight spiraling of the bullets, as depicted in the movie, is anywhere close to accurate. Maybe there’s no way to explain it to me descriptively–rather than by math–but I suppose I always thought that bullets, while traveling rapidly, weren’t also spiraling (spinning) quite as fast/tightly, as depicted.

Any way to help me on this?

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So… I think you need to get a clue and realize that it is not any of the tax payin American’s business WHAT George Bush’s Middle Eastern policy is!!! Ass holes!!!

Welcome to the Straight Dope, poopmonger. The BBQ Pit is over here.

well, that was certainly an interesting answer… For a far more dull but perhaps more on-topic one, yes, bullets spin incredibly fast, and no, they don’t spin so fast as that…

Each barrel has a twist rate, given in inches, which tells you how many inches to a full revolution of the bullet. Rifles typically have somewhere between 7 and 12 inches, iirc. Of course, given that the bullet is travelling those 7 or 12 inches in not much time at all, this works out to hundreds of thousands of revolutions per minute. I’m not sure what the spin rates for handguns tend to be, and google didn’t give them to me right away, but there’s a really cool picture here http://www.nennstiel-ruprecht.de/bullfly/fig22.htm

Anyway, to answer the question, it depends on whether Neo slowed time, or slowed the bullet travel, without correspondingly slowing the spin. In the former case, the bullet should still be turning once around its axis for every 7-12 inches of forward travel (or whatever a typical twist rate for a handgun is), at whatever apparent speed it was travelling in Neo’s time frame. In the latter case, the bullet could still be spinning on its axis at 160,000rpm (by comparison, my drill gets to 2250rpm, and a high-speed Dremel minitool tops out at 30,000), while travelling forwards at whatever speed Neo slowed it to.

My interpretation is that Neo fully realized just how artificial and computer-generated, the matrix really is. Since he now knows that everything that happens is just a bunch of code, he can hack into the system and pretty much do whatever he wants. In other words, he could make their forward motion slow down, and yet speed up their rotation, or make them rotate the other way. In short, he has freed his mind.

On the other hand, once the bullets have completely stopped, he looks menacingly at the agents, and his head-turn appears to be in real time. So that’s a possible hint that time itself doesn’t slow down, just the bullets.

Here’s an image from the film (from here). The wavelength looks to me to be maybe 4-6 inches, which is a little short of 7-12 inches.

Then here is a tiny little image of the climax scene. I think they just took the same effect, and it’s supposed to be time slowing down. I mean, if the bullets were slowed in their flight, but time continued regularly, then you wouldn’t see the waves behind them.

Slightly tangetial link, but this was something cool I was looking at earlier today:

High-speed photos of bullets doing all kinds of damage (the pictures loaded awfully slowly though, for me anyway). Bit worrying that some of those photos appear to show various current ID cards being sliced up. Still, it’s quite cool how half the card seems to just float there.

Is 160,000 rpm really accurate? I realize a bullet usually travels only for a split-second, but this seems amazingly fast.

Also, one of the links provides a graph demonstrating the “yaw” effect of a bullet. Maybe I’m misinterpreting this chart, but it seems to suggest that a bullet does not travel in a perfectly straight path but, instead, kinda corkscrews toward its target. That said, this doesn’t make sense to me.

I don’t know squat about guns, this site shows the muzzle velocity of some rifles and handguns.

If a bullet were turning 1 time in, say, 6 inches, and we divide that into, the muzzle velocity of a 9mm Lugar (1120 fps), you’d get a rate of 2240 rpm.

Well, let’s call it 7 inches, which means the bullet makes one full rotation for every 7 inches it travels forward. Let’s assume a fairly high muzzle velocity of 3000 feet per second, or 2,160,000 inches per minute. 2,160,000 / 7 = 308,571.4 RPM. If we got with 12 inches and a more conservative muzzle velocity of 1500 feet per second, it works out to 90,000 RPM.

I make that 134,400 RPM.

I think you are interpreting the chart correctly. Bullets, apparently, do have a tendency to yaw out of the muzzle, and then ``settle down’’ into a proper trajectory further downrange. Folks chasing the smallest groups possible say some rifles will group better at 200 yards than at 100, for this reason.

Not sure I can explain better than that, though. I’m chasing groups the size of a deer’s chest, and not doing very well at it, so all this talk of quater-minute-of-angle groups kinda goes over my head

A one-in seven-inch twist would be astoundingly fast. A very fast twist would be closer to one-in-twelve, with one-in-sixteen being closer to the norm for something small and fast like a .223.

A handgun, like the aforementioned 9mm, might have a 1:24" twist. Big heavy cartridges like a .444 Marlin or .45-70 might have a 1:32" twist. (There is, of course, lots of variation between manufacturers, calibers and barrelmakers.)

With small, light bullets at ultrahigh velocities (in excess of 4,000 fps) too fast a twist will actually cause the bullet to “explode” in flight from gyroscopic forces. You literally see a tiny, faint black “cloud” appear twenty or thirty yards downrange as the projectile flings itself apart.

I seem to recall reading bout an estimated upper RPM limit for a given caliber, but I can’t remember the details. Suffice to say it’s considerably below the 300,000+ rpm noted in the above example. I want to say the limit is comfortably below 100,000 rpm, but I can’t say for sure.

Yep. Bullets do rotate around a point, and do not travel with their noses pointing exactly at the target. I don’t have the report sitting in front of me, but a study done several years ago too pictures of bullets in flight on two planes to get the truw orientation of a bullet in light. Bullets pointed off their line of travel from 3-7 degrees.

If folks want, I can dig up the reference.

–Patch

The M16A2 has a 1:7 rifling twist. The older M16A1 has a 1:12 rifling twist.

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**A handgun, like the aforementioned 9mm, might have a 1:24" twist. **

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From a Sig Sauer web page, the P220 (.45) has a 1:16 twist, and the P239 (9mm) has a 1:10. You can aslo find more rifle twist rates here.

–Patch

Sorry for my being dense, but let me make 100 percent sure that I understand what you–and a link above–seem to be saying.

From what the link suggests, when the bullet exits the barrel of a firearm, the bullet not only twists (or spirals) on its axis, due to the firearm’s internal rifling, but it also actually corkscrews in flight as it speeds toward the target. By “corkscrewing,” I mean that if you we’re to look directly at the bullet coming toward you–in super-slow motion–the bullet’s flight path would resemble a corkscrew pattern, although the deviations from a straight flight would be practically immeasurable.

Correct? That’s odd, as I’ve always thought that bullets in flight, aside from falling from their flight path over long distances, went perfectly straight, (i.e. no corkscrewing or wobbling.)