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Why does a bullet tumble?
6 Answers
Frank Duncan
Frank Duncan, NRA Life. Owned firearms for over 50 years.
Answered Dec 14, 2016 · Author has 4.8k answers and 7.2m answer views
A bullet tumbles because it has lost stability. Rifled weapons spin a projectile (called a bullet) so that it has gyroscopic stability along its axis and travels point first to its target. This means that the bullet will always present its nose forward into the airflow thus increasing accuracy and retained velocity because it doesn’t turn sideways.
But a bullet will lose stability when it impacts a “soft” target and the nose is slowed causing the base to begin to rotate around the nose. Some military bullets are designed with a light nose and heavy base to accentuate this property and create a much more severe wound.
Bullets will also tumble in flight if they are not spun at the right speed. A light bullet can generally use a lower spin rate than a heavier bullet. Consequently, a heavy bullet rotating too slowly will lose stability in flight and veer in a spiral. Naturally, that will certainly ruin its accuracy.
People who reload know that there is a balance that has to be made between bullet weight, spin rate, and speed. Each rifle will have a combination which is optimum for that rifle and the only way to find it is to load different types and weights of bullets with different weights and types of powder.
Bullets can also tumble if they are fired from a barrel that is too large for the projectile. On a pistol range, I have seen targets with the hole in the paper exactly showing the outline of the SIDE of the bullet where it went through the paper. I would really like to know what they were shooting since the target looked like someone had fired a shotgun. Only a few (relatively) round holes indicated a pistol had been used. Considering the target, I’m surprised I didn’t find the weapon in the trash can!
5.8k views · View 7 Upvoters
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Anand C K Shashidhar
Anand C K Shashidhar, Author - 10X, A comprehensive Guide to Shooting (2012-present)
Answered Jan 22, 2018 · Author has 162 answers and 435.2k answer views
A lot of well experienced answers, but I will try to add.
I will still try to summarize and list out possibilities.
In Air Guns, when the pellet does not properly fit into the O-Ring where it begins its journey, (a) variations of friction on different parts of the pellets, especially the rim, (b) loss of alignment, again especially at the rim, both cause a tumble of the pellet when shot.
This is because the pellet rim expands in an improper circle, effectively implanting a tilt to the pellet when it gets into its motion thru the barrel.
Additionally, there is a weight mismatch around the center axis of the pellet/bullet. Therefore, the effective muzzle velocity is thrust in such a manner that the projectile loses its center of axis and starts to tumble.
Irregular rifling, including a blocked rifling groove, can add, apart from the rifling, am out-of-plane twist to the projectile. Holes made by such projectile, if the target is a card/paper, will be oval instead of round.
If there is a manufacturing defect in the cartridge, where the weight of the projectile is uneven around its center axis, a Jack & Jill is highly possible!
In some cases, if the breach of the gun is plenty dirty, it could case mis-aligned cartridge placement. Although this is just not common to modern guns, I have fired 303s where, after the bolt locked, I could notice inconsistency in the shots, the sound, and the grouping, with some shots seemingly go haywire on the target sheets. I may be wrong, but I figured the 6 decade old rifle had problems in having the cartridge (and projectile) sit parallel and properly with the barrel.
As mentioned by others, damaged projectiles also bear tumbles.
Lastly, if the power to weight ratio is more than what the projectile can take, which means that the weight of the projectile is either too light or there is mismatch in the balance, than the power handling drops badly forcing the bullet to go into a roll.
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Vincent Maldia
Vincent Maldia
Answered Mar 1, 2017 · Author has 8.7k answers and 4.2m answer views
This is only for bullet behavior once it hits tissue
Spitzer bullets are - due to their pointed shape - butt heavy, as in their center of gravity is a little to the back. The spin is (assuming the barrel is designed well for the bullet) enough to stabilize them nose first in air but not in denser mediums. So they tend to fly nose first in air but in tissue eventually turn around butt first
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.
PATTERNS OF MILITARY RIFLE BULLETS
1.1k views
Edward Blackwood
Edward Blackwood
Answered Dec 14, 2016 · Author has 76 answers and 66.6k answer views
The two gentlemen aside from myself have done well to answer this question, i would just like to add one more instance where any given bullet (save for two or three specific rounds, the .338 Lapua, the .408 produced by Cheytac, and maybe the .50 bmg depending on the load) will tumble.
When a bullet, fired under perfect conditions, exits ‘supersonic speeds’ it will begin to fumble.
I think it has to do with inertia, as the rear of the bullet is more massive than the fore. But i’m not an engineer, and can’t render an acceptable verdict.
Rounds made for long range shooting, like the .408 Cheytac, combat this problem well by balancing density, weight and power as well as can be expected from a man-portable system.
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Robert Carioto
Robert Carioto, I have been an avid shooter and firearms collector for over 40,years.
Answered Dec 14, 2016 · Author has 3.4k answers and 1.3m answer views
Mr. Duncan answered the question pretty well. I just want to add to what he said. Some of the reasons for a bullet to be under stabilized are: worn rifling, firing a conical projectie out of a smoothbore, an improperly cast bullet that has an air space inside it causing it to be unbalanced, a deformed bullet or a heavily fouled barrel. If you have a firearm the begins to keyhole the first thing t look at is the bore of the barrel. Most tumbling can be traced to the bore.
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Ethan Simons
Ethan Simons, Over 20 years experience with firearms
Answered Jun 27, 2018 · Author has 419 answers and 245.6k answer views
A bullet may tumble for several reasons:
The bullet was fired without enough spin imparted to it.
The bullet has trasitioned from super to subsonic speeds.
The bullet has passed through a medium that destabilized it.
Any one of, or combination of these factors will cause a projectile to tumble.
