Bullet Tractability

Blaine Fields

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San Jose, CA
I have a question that produced a lot of heat on another precision shooting site, but not a lot of light. The question is whether 30 caliber bullets are tractable or not.

Tractability is the property that allows the longatudinal axis of a projectile to remain tangent to the trajectory. In other words, a bullet may have a positive angle of attack relative to the ground as it exits the muzzle, then become level at the apex of the trajectory and finally nose over as it heads downward toward the target. Picture a well thrown football to get a perfect picture of tractability.

According to one correspondent, bullets are not tractable. He believes that whatever angle the bullet has at the muzzle the bullet will retain throughout its flight. In otherwords, the longitudinal axis of the bullet remains fixed in space from muzzle to target; it doesn't nose over. I have been unable to obtain any source supporting this view from this particular person, however.

In contrast, I believe that a bullet that is just stable at the muzzle, i.e., not overspun or over-stabalized, will follow its trajectory like a well thrown football. However, other than a mathematical reference to tractability (see this web page), I can't find any source material supporting my belief either.

Does anyone have an informed view concerning this matter? The issue is of some import, especially for long range shooting, since it impacts directly upon the aerodynamic efficiency of the bullet. If a bullet's axis is fixed in space, one would expect higher drag as the bullet began to expose a greater area to the relative wind.
 

Dave King

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Blaine

It's been a while back but I believe Warren Jensen went into a discussion about this very (not exactly named) subject. As I recall he also felt that a "well" stabilized projectily will more closely follow the trajectory path (as in your football example).

That discussion is on this board somewhere but it make take a considerable seach and a read of several to all of Warren's posts.

I believe that a statement was also made or the discussion alluded to the "fact" that an "overstabilized" projectile will not follow the trajectory and may nose up and over into tumbling/unstable flight at transition to subsonic.

All-in-all it was a very informative read.

Wishing you and all a Happy Holiday Season. /r Dave King
 

Blaine Fields

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Dave,

You're probably thinking of this discussion. However, the idea of tractability was only touched upon in passing.

Now, it may be that as linear velocity bleeds off the bullet may become overstabalized due to the slower bleed-off of angular velocity. I think that was the point being addressed by the concept of "balanced flight" bullets. But even assuming a non-overstabalized condition out to 1000 yds., the question remains: 1) are bullets tractable? And, 2) what is a source of supporting evidence?
 

Tim Behle

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Just my thoughts, with nothing to back them up. But if a bullet didn't drop it's nose in flight, then wouldn't they all keyhole on paper at long range?

I get nice pretty round holes.
 

Brent

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Jun 12, 2001
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The VV reloading manual has good information on this, I am not at home so I can't say for sure but I'll look in it tonight for what they say. It is a very interesting section in their book that explains what most never even touch on.
 

Jon A

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This subject does get complicated and I don't have enough expertise to even try to explain it fully.

But in the interest of keeping things simple, the guy that makes the blanket statement that bullets don't "nose over" is wrong. It may be possible with right combination of conditions but it definately isn't true for all bullets generally.

If you need proof, just look at people hitting things at extreme range using drop values even close to what a ballistics program predicts. This proves that the bullet has a BC at extreme ranges, while maybe not exactly the same, relatively close to what it has at short range.

At extreme ranges, if the bullet didn't "nose over" its BC would go into the toilet and it would drop like a rock. Nobody would have much luck hitting anything at ultra long ranges if this was the case.
 

Jon A

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That's interesting S1. By how much do they do this--I know that's a pretty general question, just looking for a ballpark figure--a tenth of a degree, a half, etc?

Have you ever seen anything documented on a bullet that kept the same attitude as the bore? If so, what happened to its BC at long range?
 

Blaine Fields

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San Jose, CA
Thanks, thanks, thanks.

However, this section doesn't explicitly address the tractability issue, although it clearly implies it with the analysis to the pitching moment.

Your suggestion regarding the supporting references is a good one and I'll go there next.

By the way, for anyone who has followed this thread this far, you may be interested in
this graphic which shows the fast and slow oscillations of the bullet tip as it trys to stabilize.

[ 12-23-2002: Message edited by: Blaine Fields ]
 

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