I´ve seen many camera-gun footages of WWII airplanes firing their guns, and sure enough the tracing bullets wobble like crazy; it´s actually very weird.
OK, now I in turn am confused. Does the whole bullet wobble? That defies my understanding of physics. Surely, the center of mass of the bullet follows a straight (well, parabolic, really) path, but parts of the bullet (like the tip) might well wobble around that. So if I was Neo watching slow-mo bullets coming at me, they would not form a corkscrew with a void in the middle around which the bullet in its entirety were moving, but rather there would be a path along which there would always be bullet present, but the tip of the bullet might at any given time be off a bit, with the tail therefore correspondingly off a bit in the other direction?
Ah, the joys of describing a three-dimensional object travelling in four dimensions, using nothing but ASCII text…
Well to answer your question with some field experience. Once while out rabbit hunting with a .22 magnum pistol I had the unfortunate luck of having a bullet graze the palm of my hand. I won’t go into the details about how this happened just focus on the results.
When the bullet traveled across my palm it was less than an inch out of the barrel. Besides the gunpowder burns in my palm I had a uniquely shaped piece of lead running through my hand just under the skin. The bullet peeled off its outer layer as it passed through my hand leaving a perfectly shaped corkscrew of lead. I removed the “corkscrew” by just reversing it back out of my hand where it entered. I cleaned up my injury with a little antiseptic soap and let it heal normally. To this day the only remnants I have from this injury are a few very small unburned gunpowder pellets lodged just under my skin along the path the bullet traveled. They are too small to worry with.
So to answer the original OP yes bullets do spin quite fast. The “corkscrew” I pulled out of my hand had about 20 revolutions over a distance of 3 inches.
They do slow down in their spinning the further downrange they travel and begin to tumble end over end kinda like a toy top will do when it begins to lose its spinning momentum. I know this because I was hit in the calf from a bullet which had traveled quite a distance. In this case the bullet tore a jagged path through the fleshy part of my right calf muscle. The shooter was approximately 150 yards away and again it was a .22 cal bullet. My wound looked somewhat like someone had stuck a screwdriver in my calf and then spun it around to widen the hole. The entry hole was shaped like a cresent moon and an exit hole looked like a trap door because the skin and muscle was hanging and able to flap open and close.
Again some field first aid, a little cleaning and an ace bandage was all it took to clean up the wound and other than a small scar on either side of my calf no other permanent damage. I did recover the bullet but when it went through my calf it flattend out to about the size of a dime. It was conicle shaped with the base pushed in and to the side and the bullet core inverted kinda like a mushroom leaning to one side.
Ale: Methinks the “wobbling” of tracers from the gun camera footage is due to the vibration of the camera, not the bullet itself.
I did RPS instead of RPM. :smack:
That’s what I get for SDMBing on a laptop while my kid watches Scooby Doo on my lap.
That’s right. This is more or less what I said in my previous post.
Oh god, won’t someone think of the children???
Ok, a follow-up query. If bullets ( s.i.c. ) travel in a wobbling fashion but at very high speed, how is that trajectory and wobble affected by moving rapidly through air?
( Theoretical- I hate guns, but this came up the other day in conversation ). If you are driving 70 mph down the highway and you fire a gun at a sign along the side of the road, is the air rushing by the vehicle going to have such a significat impact on the path of the projectile that you won’t hit it? All things being equal, and assuming you would have hit it if standing still, I mean. Or is the forwards force SO great, that the airstream moving by as it exits the weapon and enters the airspace outside of the car not a significant factor?
The outer surface of a 5mm diameter bullet, rotating at 100,000 rpm would experience a force of 27,950 gravities, at 134,400 rpm, the force would be 50,487XG. That does seem a bit much for a chunk of lead.
Like this? (from link posted above)
This linked diagram seems to describe this corkscrewing or “precessing” effect, and suggests that it tames down over distance. Correct?
As to the previous poster who claims bullets “tumble” end over end toward the end of their flight. I’ve heard similar claims of the .223 mm M-16 projectile. Frankly, I have a difficult time believing a tumbling bullet would be accurate, since “tumbling” is hardly aerodynamic.
I might add that, prior to this thread, I thought the only corkscrewing (“precessing”) was found in unrifled muskets, producing sometimes wildly inaccurate shots.
Sidenotes. Not neccesarily relevant, but…
-You can see some bullets in flight (.45 ACP comes to mind, watch your buddy shooting next time, and watch for the bullets. Cool stuff.)
-When shooting long range, have your buddy watch for ‘trace’. The vapor trail the bullet leaves behind is visible through clear spotting scopes. Again, cool stuff.
Bit more relevant: The AR-15 Forums Ammo FAQ.. Also, if your bullet is tumbling before it hits the target, you have serious issues with your rifle, your ammunition, or both.
I’ve never had a problem hitting a target while traveling at 70mph down a highway. Its even easier when you use a machine gun!
A bit of the off subject thread, but I saw “Kill Bill” this evening. There was one of those outrageously expensive CGI shots of a bullet being chambered, fired and traveling in the air. There was no spinning involved…or wobbling.
If you can’t trust Hollywood, or Terenteno for that matter, who can you trust?
On a more serious note: Does a bullet actually follow the rifling grooves exactly. Wouldn’t this greatly reduce muzzle velocity. (added friction and force needed to leave the gun) perhaps even cracking or blowing up your barrel? (like a speck of dirt or snow)
I’ve always understood the rifling in a barrel to generally get the projectile spinning. To coax the bullet to spin instead of dictating its spin, to put simply.
To say that a barrell’s rifling specific spin rate is one spin every 7" is not to say that the bullet will follow that spin rate but one of a much lower RPM rate. Is this an accurate statement? I’ve grown up with guns and hunting and target practice but have no scientific background in ballistics. This is just a common sense assumption.
Correst. The 5.56mm bullet fired by the M-16A1/A2 does not tumble in flight.
Much of the mythology surrounding this bullet I believe stems from the fact that people hear that the bullet tumbles in the target. What folks don’t know is that any bullet who’s center of pressure is ahead of the bullet’s center of gravity will tumble when travelling through tissue or a similar dense medium. And the word tumble is more correctly defined as “rotating 180 degrees whereupon it will continue to travel base-first (it will not continue to rotate end-over-end)”. Research papers I’ve read describe this movement as a “yaw” to avoid confusion. Even FMJ pistol rounds can do this.
The 5.56mm bullet (whether the older M193 or the newer M855) will rotate 180 after travelling roughly 10-12cm (average) before rotating. If the bullet is travelling faster than around 2500fps, it will fragment at this point, creating multiple secondary wound channels which are intensified by the temporary cavitaiton stretch. (This is the problem with the short-barreled versions of the M-16: the muzzle velocity is too low to fragment the bullet).
Off the top of my head, the 7.62mm bullet fired by the AK-47 will begin its yaw cycle after about 30cm. The 5.45mm bullet fired by the AK-74 begins after 3-5cm. Neither of these fragment, however.
If you go downrange at a firing range with dirt berns, you can pick up fired bullets from the ground and examine the rifling marks. If a bullet were slipping through the rifling, you’d see evidence of this. I never have.
Check out the photos on this page. Notice how well-defined the rifling grooves are. If the bullet were “slipping” past the lands, as you suggest, I’d expect the grooves to be more smeared out and indistinct.
Aim low and remember to lead a little more than usual. Oh, wait. That wasn’t what you meant…
Crosswinds can affect the trajectory of the bullet, so yes, a 70mph crosswind will affect the bullet’s impact point. Remember this when shooting at that speed limit sign.
It is. Handloading manuals have such warnings. Bullets intended for .22 hornet have a thin copper jacket so they will expand properly in game targets at the relatively low velocities of that cartridge. Using that bullet in a .223/5.56mm cartridge with a much higher muzzle velocity and spin rate can cause the bullet to actually come apart in flight.