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Bullet Tumbling?

Discussion in 'General Gun Discussions' started by MGSfan, Dec 9, 2004.

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  1. MGSfan

    MGSfan Member

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    Hi, I'm new to these boards and I have a question:

    I have heard both sides of this argument and would just like to know, is it possible for a bullet to tumble in flight?

    Again, I have heard that it does and that it doesn't. If you could provide a link where I could find reliable information it would be much appreciated.

    Thank you. :)
     
  2. zahc

    zahc Member

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    It's possible, but never desireable.
     
  3. benEzra

    benEzra Moderator Emeritus

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    It will always occur if the bullet is understabilized. A bullet's center of mass is behind the center of aerodynamic drag, so that if you were to throw a non-spinning bullet at high velocity, it would turn and eventually stabilize base-first. However, bullets fired from rifles and handguns are spin-stabilized, which keeps the bullet going nose first. However, if the bullet is launched from a barrel that spins the bullet too slowly for proper stabilization (like shooting a 77-grain .223 bullet out of an older AR-15 optimized for the lightweight 55-grain rounds), the bullet may begin to tumble in spite of the spin. You can tell at the range by the sideways bullet holes in the paper (i.e., hole in paper is elongated).

    This is very bad from an accuracy standpoint because as soon as the bullet starts to turn, aerodynamic effects come into play that shift the bullet's flight path erratically, and accuracy goes out the window.

    Here's an excellent resource on ballistics (and firearms physics in general): Understanding Firearm Ballistics (book)
     
  4. mete

    mete Member

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    Without stabilization from spinning the bullet will tumble but if it does there will be no accuracy. The bullet weight [actually length] determines the rate of twist necessary. The longer the bullet the tighter the twist necessary. Typical twist for the 223 goes from1 in14" to 1 in 7". Some military rounds have been designed to be stable in air but when they hit a person they become unstable and tumble. An undersized bullet may tumble . A bullet fired from a barrel with heavy lead deposits may tumble.
     
  5. Kramer Krazy

    Kramer Krazy Member

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    Just this past Saturday, I noticed that my Taurus PT-22 (2.75" barrel) was spitting a few bullets out and they were starting to tumble (sideways penetration in the paper/cardboard). This was at about 15 yards without any obstructions. I just figured the gun was fouling up and the bullet wasn't stabilizing. Also, when I could shoot my guns in my parent's back yard, I recall several times having my .223 from my AR-15 ricocheting and tumbling through the air. It made an interesting and distinctive whistling noise.
     
  6. Valkman

    Valkman Member

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    My Carbon-15 .223 pistol tumbles bullets, and I'm not sure why. I'd guess about 50% do it and I wasn't shooting from more then 10 or 15 yards. I wonder if a bigger bullet would help? Not that I shhot the thing much - if I wouldn't take a huge bath on it I'd sell it. :p
     
  7. P95Carry

    P95Carry Moderator Emeritus

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    My Mini 14 (1:7 twist) hates Russiam ammo - and even at 25 yds there is evidence of tumbling ... danged if I can see why tho I haven't as yet mic'd the bullets to see if undersize at all. Use American Eagle for example and things are relatively normal.

    Tumbling is never good ballistically - only when the bullet is ''working'' on a wound channel does tumbling get (macabre hat) ''useful''!!

    The R9 9mm pocket pistol can produce tumblers with the wrong ammo - not a fault of the gun when you have to consider in its design it has a full 1/4" freebore. That can mean that with a round loaded to short OAL, there is enough time for a bullet to go slightly off axis before engaging the rifling - and then engrave slightly asymmetrically. Mind you, at close (defensive) distances this is hardly a major problem either, should it occur.

    Don - surprised at that Car-15 problem .. any ammo? Or one sort in particular? Mike B has one and we shot it at a shoot in East PA not so long ago - don't remember any tumbling issues - but wonder if he can comment.
     
  8. nemesis

    nemesis Member

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    Several members have mentioned here that they are experiencing bullet tumble at fairly close distances. I doubt it.

    "Keyholed" targets are most often torn targets. Some types of paper, under certain conditions (humidity?) tend to rip and look as if the bullet keyholed.

    You can prove or disprove this notion by firing through something more solid. Like heavy cardboard, ceiling tile or anything fairly rigid.

    Keyholing is fairly rare.
     
  9. P95Carry

    P95Carry Moderator Emeritus

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    nemesis - agreed it is (thankfully!) quite rare but - instance my mention of Mini 14 with Russian ammo ...... at 25 yds and not much more ... a target can have a ''sideways'' bullet entry!!! No way is this an unequal paper tear - it is a clean profile of a side on bullet! Normally of course with 22 cal .. nice clean hole!

    I agree - with larger cals and slower bullets ... FMJ round nose classically - unequal tears can often look suspect when not.
     
  10. g56

    g56 Member

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    A long time ago there was a fad of loading hollow base wadcutter bullets upside down for 38 special, it makes a mean looking hollow point, but the bullet is extremely unstable, I've seen many of them go through a target sideways, the hole in the target is quite obvious and shows the bullet is tumbling, and this happened quite often when loading that way. Fire 5 shots out of a Chief's Special at 20 ft and you would have 5 different shaped holes!

    I have seen both rifle and pistol bullets going through targets at an angle or sideways, again the bullet is yawing or tumbling, this doesn't happen very often, but most often if the twist of the rifling and the weight of the bullet aren't compatible.
     
  11. Rotnguns

    Rotnguns Member

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    Actually, bullets will wobble for a short distance after they leave the muzzle. If they have both gyroscopic and yaw stability, the wobble will die out quickly. If not, the wobble gets worse and the bullet goes into a genuine tumble.

    Since bullet velocity causes forces which tend to perturb stability, and bullet spin promotes stability, bullets which start out stable actually become more stable as they go downrange (spin rate slows at a much slower rate than downrange velocity).

    It's interesting that the most stable bullet shape is a disk!

    Modern Exterior Ballistics, by McCoy, is an excellent text on the subject.
     
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