[The Silver Bullet 1719]

I have always heard the 5.56 NATO and 5.45X39MM bullets will tumble either in mid-air or when it hits a target. I don't see how the bullet would do it in mid-air, but what about when it hits a target? Is all this just a battlefield myth or is there truth to it?

[Monte Harrison]

Tumbling in mid air is a myth. Rifle bullets at high velocity hitting flesh to tend to immediately go wildly unstable inside a body, and may flop over and even tumble, but this only happens AFTER the bullet has entered the body.

[Mal H]

Tumbling of the NATO rounds as Monte says is a myth - a media myth.

However, tumbling of bullets is not necessarily a myth. It can be caused by a relatively slow twist rate combined with a heavy and slow bullet. The bullet isn't stabilized during flight and will wobble or even tumble if the instability is extreme. You can see the evidence from "keyholing" in a target. This happens more often with handguns than rifles, but in either case it is important to match the load to the gun. Commercial ammo will rarely tumble unless a rifle has an unusually slow twist rate for the particular caliber.

[MrAcheson]

IIRC the reason the 5.56 round was changed is that it tumbled a little too readily. A bullet shouldn't tumble in mid air unless it hits something, but the 5.56 had a reputation for going unstable at the smallest provocation like going through light ground clutter. When it hit a person it would tumble as well, which is a good thing because then the bullet does more damage. The military increased the twist rate of 5.56 barrels to help with the former but unfortunately they seem to have hurt the latter.

[Jim Watson]

"Tumbling" is kind of a sensationalistic term meant to give you the impression of a bullet spinning end over end like a buzz saw. The technical term is "yaw."

The Army found that M193 55 gr FMJBTs were not stable in cold, dense air and increased the rifling twist from the 1 in 14" of the .222 to 1 in 12". This was done to keep cheap FMJ bullets from yawing to the point of losing accuracy or completely keyholing - hitting the target sideways (If you can find where it hit at all.) It had to be increased again for the heavier, longer, M855/SS109 bullets. A 1 in 9" would have been enough for ball, but it took a 1 in 7" for the very long tracer bullet. Which worked out, they knew what to expect when they started loading 80 grain bullets for long range target shooting.

There is NO practicable rifling twist that will keep a spitzer bullet point-on in dense material - like flesh. Which is why dangerous game bullets are roundnose and you can read many old safari stories of failures with cheap surplus .303 British Mk VII spitzers. But the bullet does not tumble in buzz saw fashion. It (usually) yaws over until it reaches a stable position and stays that way. Pictures of gelatin blocks and high speed photos show that a lot of bullets will exit (Or come to a stop if the target is big enoug.) in a base-forward position. So a bullet that yaws "only" 180 deg - half a turn to base first - will have been going through the target - maybe YOU! - sideways at one time. Ouch. In the meantime it has been turning through some angles that can deflect it so the wound track is not straight. Maybe worse Ouch.

That is, if the range was not close enough and the striking velocity high enough for the bullet to break up. Double Ouch.

I go with the position that the loss in "stopping power" is not due to too stable a bullet to "tumble" but due partly to the heavier and slower bullets but especially due to the handy CAR15, XM177, and M4's bad concept of drastically shortening the barrel of a rifle that depends on velocity for effectiveness.

[telewinz]

As any reloader will know, bullets WILL tumble in flight. It is the result of a mis-match in rate of twist of the rifling versus bullet weight. Their are other causes such as too soft a lead bullet being propelled too fast and not gripping the barrel's rifling. How can you tell if your bullet is tumbling in flight? Look for "keyholing" on your paper target.

[gun-fucious]

http://www.fen-net.de/norbert.arnoldi/army/wound.html

PATTERNS OF MILITARY RIFLE BULLETS
(by Martin L. Fackler)


The distance that the military-type bullet travels point-forward before yawing is critical to wounding effects. The distance shown on the wound profiles is the average distance at which this occurs. However, it is important to recognise how much shot-to-shot variation from this average distance can be expected. Taking the M16 wound profile (Fig. 6) as an example, it shows significant yaw starting at a 12cm penetration depth. Seven out of ten shots can be expected to begin yaw within 26 per cent of this distance (between nine and 16cm penetration depth).


Military rifle bullets yaw in tissue because their rotation is sufficient to maintain their point-forward travel in air, but insufficient to maintain that position in tissue - sooner or later they yaw to reach their stable centre-of-mass-forward attitude.

[BigG]

The same reason a raindrop looks like it does, heavy rounded end down and pointy end last is the reason bullets eventually turn around in flesh. The heavier end will eventually lead the way.