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Thread: Bullet wobble

  1. #11
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    From the first page on google;, and there are many many more very informative articles.

    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.
    2.8k views View 2 Upvoters
    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.

    1.3k views
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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.
    Last edited by jaycee; July 20th, 2019 at 09:04 PM.

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  3. #12
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    Shooting full form bullets out of a smokeless ml has taught me much over the past years. One thing that has significant impact on this seems to be rifling and bore consistency.

    The most consistent bore and rifling produces next to no wobble or change in accuracy over broad range of velocities.

    In other words I can push a 200 or 300 grain bullet from 2000 to 3000 feet per second with no discernible wobble and only minor accuracy changes.

    Indeed I actually can choose my preferred velocity based on bullet construction.

    Conversely, we have had two match barrels with some inconsistencies and those barrels tend to produce really accurate groups as well but not over a range of velocities.

  4. #13
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    Quote Originally Posted by Big Jack View Post
    The most consistent bore and rifling produces next to no wobble or change in accuracy over broad range of velocities.
    You're right Jack...I was shooting .58 Minnie ball at 50 yds thru a variety of loads (40 gr -80 gr) and had a terrible case of keyholeing. Turns out the 'skirt' on the Minnie's I had bought were not thin enough to expand into the rifling. So the bullet was not engaging the rifling and was rattling down the barrel.

    For those who haven't seen what we're talking about...the pic below shows what keyholeing looks like, the hole just right of the twoonie is pretty close to normal.

    Last edited by MikePal; July 21st, 2019 at 07:35 AM.
    Arte et marte (By Skill and by Fighting)...The RCEME motto

  5. #14
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    It’s interesting. No grab of rifling and all goes to heck.

    I can think of another good example when considering the 204 Ruger rifles I’ve owned.

    The first was a beautiful savage model 12 target. It would stabilize 32 grain pills well but 40 and 45 not so well. 39 pills worked well.

    The next couple I owned were T3’s in lite and Varmint. They would stabilize 32,40, and 45. The next one after that was the same in stainless lam.

    Same darn twist rate but it all comes down to the barrel IMO.

    Personally I think that’s why Sako and Tikka offer 1 MOA guarantees.

    The CZ 204 was good as well that I had.

    A good friend of mine also bought a savage right around same time I did. Same results.

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    Quote Originally Posted by Big Jack View Post
    It’s interesting. No grab of rifling and all goes to heck.

    I can think of another good example when considering the 204 Ruger rifles I’ve owned.

    The first was a beautiful savage model 12 target. It would stabilize 32 grain pills well but 40 and 45 not so well. 39 pills worked well.

    The next couple I owned were T3’s in lite and Varmint. They would stabilize 32,40, and 45. The next one after that was the same in stainless lam.

    Same darn twist rate but it all comes down to the barrel IMO.

    Personally I think that’s why Sako and Tikka offer 1 MOA guarantees.

    The CZ 204 was good as well that I had.

    A good friend of mine also bought a savage right around same time I did. Same results.
    That just goes to show you that each rifle has it's own preference for the bullet that shoots well out of it, my buddy and I have identical rifles of the same .243 cal, what is accurate in his is terrible in mine and vice versa.

  7. #16
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    If your bullet is not to long ...
    then you will not have a problem
    Your bullet will spin and not Wobble

    Unknown.jpeg


    Quote Originally Posted by gbk View Post
    Hi guys!

    In one of the threads someone mentioned bullet wobble ,and that it tames after 100 yard.
    Interesting topic.
    Could someone tell me more about this,"anything"is new to me,I am not quite familiar with this phenomenon.
    Mostly interested in 243,30-06 and 20 g sabot.......

    Thank You

  8. #17
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    Quote Originally Posted by alfoldivandor View Post
    If your bullet is not to long ...
    then you will not have a problem
    Your bullet will spin and not Wobble

    Unknown.jpeg
    That’s not really a blanket statement that holds true.
    Light for caliber(or more correctly generally shorter for caliber) bullets can be over stabilized in a fast twist barrel designed for longer/heavy for caliber bullets,just as longer bullets won’t be sufficiently stabilized in a slow twist bore.
    ie;if you are driving 45gr .224 bullets @3400fps down a 1:7 twist designed to shoot heavy for cal 80,90 even 100gr bullets available now,you could experience jacket separation for one thing.The higher velocity of a light bullet in a fast twist can also increase barrel torque which opens up group size.
    Also,shorter bullets are inherently more susceptible to minor manufacturing flaws and variables such as being slightltly off balance,which will be exaggerated by a combination of both the faster then necessary twist combined with higher velocity,causing wobblers and fliers and a drop in overall accuracy.
    The best advice is to use the slowest twist necessary to stabilize the desired bullet.
    If there was a perfect compromise twist that shot everything well,there’d be no need for faster twists to stabilize longer bullets,and slower twists for shorter bullets,they’d just build a fast twist for everything?Theres always some give and take or compromise,no one twist rate will accurately shoot the entire range of bullet weights and lengths in any given caliber.
    Last edited by Grinr; July 28th, 2019 at 03:04 AM.

  9. #18
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    Quote Originally Posted by Gun Nut View Post
    There is a yaw shown in Lyman Reloading Handbook 45th Edition. The yaw imparted to the bullet during the spinning around the axis of flight may be caused by excessive velocity or the wrong combination of twist to bullet length. Bullets that yaw in this manner in early flight sometime settles down and spin true as they lose velocity.

    They use the term yaw I called it wobble. A bullet when it leave the muzzle may not stabilize immediately, there are a number of factors that can cause this to happen the illustration mention a few. Eventually they usually stabilize and fly true. The distance it take this to happen can vary from gun to gun and possibly from one bullet design to another. I mention my .303 British it seem to take about 100 yards with the bullet I was using to stabilized. At one point I was loading a cast spiral tip with the recommended Unique load of powder. The bullet was key-holing at 25 yards. I switch to a reduced powder charge of IMR 4895 and it stop the bullet from key-holing. The general accept idea is they put rifling in the bore in order to spin the bullet which off-sets the influence of gravity. What I discovered was spin has another variable which is velocity. The speed that the bullet travels through the rifling determines its rpms. If the rpms are not adequate the bullet will not stabilize and will end up tumbling, If its rpms are a bit high it will yaw, but as the bullet slows in flight it generally stabilizes. Im not a ballistic expert, so there maybe other factors involved.

    You dont stop hunting because you grow old. You grow old because you stop hunting.
    - Gun Nut
    Im not a gun expert but I understand that the .303s are notorious for having inconsistent barrel diameter due to poor machining practices back in the day. I remember being at the range on day and the guy next to me was shooting a .303 and was key-holing at 100 yards. Turns out his barrel diameter was too large for the bullet he was using,

    I quickly realized when I started reloading that you have to account for rifle twist when working up loads. As you alluded to, if you dont get it right, your bullet wont fly true,

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    interesting story ...that "salesperson" was either trying to get rid of "overstock" round nose bullets or was not knowing about guns & ammo !.....the standard 1 in 10" twist of the 30-06 will stabilize bullets from 100gr plinkers to 220gr round nose torpedos at velocities attainable with the 30-06 ... as a note ... Hornady loads their SSTs (150gr, 165gr & 180gr) in their Superformance line at top velocity (safe in the 30-06) - I'd be reluctant to shop in that store again !!!

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