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  1. #1
    RugerCal480
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    What causes a bullet to tumble or keyhole??

    Just got in from shooting a 336 RC, 35 Remington, that I bought used. Shooting 150 grainers at 50 yds. holes in the target were almost perfect. Using Winchester and Remington 200 grainers....both tumbled and keyholed at 50 yds and 100 yds. Slashes were about an inch and a half long. I returned the rifle to the place that I bought it and they had me leave it for the gunsmith, along with the four targets and two samples of the 200 grain bullets used. The bore is clean and the micro grooves still have a great deal of depth. The crown is good. It looks like the action might be feeding the 200 grain bullets in too far so that they touch the lands. The 150s are more pointed; the 200s are round nosed. The two sales fellows, both knowledgeable, want the gunsmith to look at it, using fingernail polish to see how far it feeds into the bore and if it is touching the lands, and said, there is an adjustment on the Marlin 336's that can correct the amount of feeding that takes place. Anyone with any experience on that end know of this happening before, or having adjusted the action in their own gun to correct such a problem? or what causes a bullet to tumble?? Thanks.

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    What causes a bullet to tumble or keyhole??

    First thought was crown, second undersized, third is rate of twist not sufficient to stabelize the length of the bullet.
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  3. #3
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    What causes a bullet to tumble or keyhole??

    Or Rifleing all plugged up with lead , smooth bore instead of grooved
    Gunjunkie..

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  4. #4
    RugerCal480
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    What causes a bullet to tumble or keyhole??

    hmmm....given my situation: why would the 150 grain bullet spin properly (clean holes, thus gripping the micro-grooves)and the 200 grain bullets not spin and tumble instead?

  5. #5
    FWiedner
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    What causes a bullet to tumble or keyhole??

    Sure-Shot has the answer, seems like it's gotta be a, b, or c.

    .35's usually love those 200gr bullets.

    You said you bought it used, maybe somebody trashed the bore with an ambitious hand-load and then sold it off. See any odd "rings" while inspecting that bore?

    :?

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    What causes a bullet to tumble or keyhole??

    Quote Originally Posted by Sure-Shot
    First thought was crown, second undersized, third is rate of twist not sufficient to stabelize the length of the bullet.
    99 times out of a hundred, tumbling occurs when bullets aren't spun fast enough. The heavier the bullet, the faster spin it needs.

    Shum8
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  7. #7
    RugerCal480
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    What causes a bullet to tumble or keyhole??

    There were no unusual "rings" in the bore ....the bore looked very bright and shiney and the grooves appeared to be deep, .e.g., there were no visible places where the grooves disappeared or where the bore was solid shiney/bright...the bore light did not indicate any problems there...I didn't use a bore foam on the micro-grooves and the folks at the gunshop didn't see any indication that they were dirty or clogged in anyway. THe crown was not chipped in any way or worn unevenly. As I mentioned....they thought the 200 grain bullets were longer than the 150s and loaded into the chamber with the tips pushed up against the lands.

    My own look on the internet turned up these:
    There are three reasons why a bullet tumbles after leaving the barrel:

    * The bullet's base is cockeyed and gas escapes off one side before the
    other as it leaves the muzzle.

    * Something really unbalanced the bullet as it was going down the bore.
    After exiting the muzzle, it tumbles.

    * The bullet is spinning way too slow as it leaves the muzzle; it won't
    gyroscopically stablize. Or it's spinning too fast; its natural
    unbalance creates enough centrifugal force to cause it to tumble.

    and this:

    A properly stabilized bullet (that is, one spun with sufficient rotational speed by the rifling) does not tumble in flight, but may tumble upon impact with a soft target. If a bullet were to actually tumble in flight, its accuracy would be so bad as to be unusable. What does happen is, that due to aerodynamic lift on the bullet and minute inconsistencies in the location of the bullet's center of gravity, that the bullet's point may precess slightly, that is move about the centerline of the bullet's flight, but the bullet remains point forward. This precession is quite small and if the rotational speed of the bullet is optimum the point precession dampens out to a negligible amount in a process known as "going to sleep."

    1) I think either the micro grooves are partially clogged/dirty ...there is more lead from the round nose bullet dragging than from the 150 grain, more pointed bullet;
    or 2)the bullet may actually be touching the lands (between the grooves) before being fired, and is "unbalanced" as it proceeds down the barrel. (a head space problem?)

    I won't know what is going on for sure, until I hear from the gunsmith...but...I'll post his "verdict" when I hear from him. It is a puzzlement! :lol:

  8. #8
    Gun Wizard
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    What causes a bullet to tumble or keyhole??

    I think Sure-Shot probably nailed the problem with the first two ideas.

    Even a 200 grain bullet is short enough not to need a lot of spin - unless it is also not moving fast enough in velocity. If a bullet is close to its minimal rotations/distance ratio, it can sometimes stabilize properly or not depending on its velocity. IOW, it needs certain rpms (rps) to have gyroscopic stability. For example, a 22-250 may be able to stabilize a certain long/heavy bullet with a 1-14" twist while the same bullet in a 222 with the same twist rate barrel may not stabilize. Both bullets spin at the same rate but the lower velocity bullet is also spinning slower which prevents it from being stable. That may be the problem with that 200 grainer. Is your barrel short and/or do you know what velocity you're getting with those 200s?
    45-70, 350 NorthFork 45-70, 350 Speer 30 WCF, 170 Core-Lokt

  9. #9
    Sidewinder
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    What causes a bullet to tumble or keyhole??

    Measure the bullets and see if there is any difference in the bullet diameters. Undersized bullets aren't unheard of. Microgroove rifling, only from what I've read, may require slightly larger bullets to shoot well. Don't let anyone change your rifle until you check the bullets.

  10. #10
    RugerCal480
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    What causes a bullet to tumble or keyhole??

    direwolf - I will measure the bullets dia. and the OAL of the cartridge this evening.

    Golsovia - the barrel is 20 inches, (the mag tube also extends to the end of the barrel) I believe (I don't have the gun here right now.) and the rifling is 16rh twist, micro-grooving. I will go to the gunsmith's and check it tomorrow. As I said before, the Crown is not damaged, or chipped. As to the spin on the bullet....why would it shoot well with the 150 gr. and so horribly with the 200 (two different factory loads...both keyholed at 50 and 100 yds) if the rifling was deep, no shiny areas or indication of wearing and the barrel and twist are the standard sizes that others shoot well with? Perhaps the bullets are undersized...I will check that shortly, but even that seems highly unlikely (to me) for two different factory loads from two different manufacturers. Of course, starnger things have happened....but...
    The gunsmith will not make any changes without talking with me...he is to see if he can diagnose the problem for the present. It should be under the store warranty as it is less than a week old since the purchase.

    I am not trying to be argumentative with possible ID of the problem (and I hope that is not anybody's perception of my responses)...just trying to understand why/how it could be. I do appreciate the input


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