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From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: 22-250 or 223 Savage 110GV vs. Ruger M77???
Organization: Hewlett-Packard Fort Collins Site

James Warren (jdw@unislc.slc.unisys.com) wrote:

: Another strange problem I have encountered with mine is that if you shoot
: match bullets with H-380 powder, they will tumble. ..........
: ....... I have talked to the technicians at Hornady and Hodgdon and they
: both had seen the problem but neither could explain why it happens.

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.

I doubt if the first and third reasons apply to your situation with H380.
That leaves the second one; something is unbalancing the bullet before it
leaves the barrel.

If other bullet-powder combinations shoot very well, then the difference
between those and the H380-match combinations is the powder and bullet.
If those same bullets shoot well with other powders, then it's the H380.

The only way powder can cause a bullet to be unbalanced before it leaves
the muzzle is for it to change the bullet's shape.  One way that can
happen is the powder is just barely ignited and not completely burns.  You
can determine this if the bore is very, dirty after shooting H380, but much
cleaner after shooting other powders.  If there's enough powder residue in
the bore to distort the bullet as it rides over the clumps of powder
fouling, that could cause the bullet to tumble.

One solution may be to use a hotter primer with H380 powder.  That'll
help burn the powder more completely and reduce, if not eliminate, powder
fouling.

The other way powder can change a bullet's shape is that it burns so fast
initially, it slams the bullet into the rifling too hard and the bullet's
rear part enlarges in diameter non-uniformly as it starts into the rifling.
But this typically just causes larger groups, not keyholing bullets.

I'm surprized neither Hornady or Hodgdon could explain why such things
happen.

BB


From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Tumbling bullets from reloads
Organization: Hewlett-Packard Fort Collins Site

Jerry Bransford (jerryb@jerber.sandiego.sgi.com) wrote:

: Once in a while I see elongated holes in my targets, which I assume is from
: the bullet tumbling while in-flight.
: Anyone have an idea which area of the process I should look at that would
: be the probable/reasonable cause of the bullet to tumble while in flight?

Bullets typically tumble in flight from a single cause; the base of the
bullet is not square with the bore/muzzle when it exits.  This happens
more often with handguns using cast lead bullets.  As cast lead bullets
are easily damaged by being bulk packed or handling, any dent on the
perimeter of their base will let gas escape at that point before the rest
of the bullet's base clears the muzzle which can cause the bullet to be
tipped as it leaves.

Once in a while when the shorter bearing surface handgun bullets are
seated in a case, they will be cocked quite a bit.  As they won't get
straightened out enough when they're fired and enter the rifling, their
crooked base now causes the same problem mentioned in the previous
paragraph.

About the only time rifle bullets tumble is when they aren't spun fast
enough when they leave the muzzle.  Spin rate is determined by velocity
and rifling twist.  But this rarely happens.

BB

 
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