Transonic, Stability & Tractability

[GunnyGene]

This is a very interesting video about extreme long range shooting and balanced projectile flight.

How far can a rifle shoot effectively? How does the .408 Chey Tac attain balanced flight? What twist rate is best for extreme long range applications? To answer these questions, there is an outer barrier to be aware of. Your maximum effective range may be limited to your max super-sonic range depending on how well your bullet passes through the transonic zone.

In this video, Rex discussed the behavior of a rifle bullet passing though he transonic zone. The transonic The Transonic zone lies between about Mach 1.2 and 0.8.

The Centre of Pressure (CP) of most bullets shifts around as the angle of attack changes and as velocities decays. The CP experiences a dramatic shift when it crosses the sonic barrier. This shift negatively affects the (dynamic) stability of the bullet. This loss in dynamic stability can cause significant shot dispersion in which coning motion starts, & if it is not damped out it may encounter uncontrollable tumbling. Mathematically correcting for the erratic ballistic behavior of bullets that have passed through the transonic region is extremely difficult. Air density also has a significant effect on dynamic stability during the transonic transition. Thus, thin air poses less of a problem.




Tractability

Tractability factor characterizes the ability of the projectile's longitudinal axis to follow the bending trajectory. The tractability factor is proportional to the inverse of the gyroscopic (static) stability factor. The greater the static stability, the lower the tractability factor -- which can often translate decreased dynamic stability at extreme long ranges.

Balanced Flight

Balanced flight technology utilizes a combination of both projectile profile and special rifling design that ensures the bullet's rotational rate decays proportionally to the decay of its forward velocity. This loosens up the bullets axis of rotation downrange so that its nose can stay on track with the line of trajectory throughout the descending leg of the parabolic arc. If the bullet is still pointed nose on with its direction of flight, it will be less apt to deflection and tumbling when it encounters the turbulence of the transonic zone. This is what enables the .408 Chey Tac to retain its precision capabilities well beyond it super-sonic range.

[youtube]http://www.youtube.com/watch?v=Ijd3cD7iQpA&list=PLJUaiRIEduNXoal2_PkBZi0vDCIcEPxUn&index=75[/youtube]

 

[John A.]

This is a subject that I really like.

I know a lot of 22 rifle competition shooters will only shoot subsonic ammunition, and most subsonic ammunition are labeled as "match ammo" because of the instabilities created when a round goes transonic/supersonic.

 

[GunnyGene]

This is a subject that I really like.

I know a lot of 22 rifle competition shooters will only shoot subsonic ammunition, and most subsonic ammunition are labeled as "match ammo" because of the instabilities created when a round goes transonic/supersonic.

Let me know what you think of his explanations about this. There's also a couple earlier videos that ease into this, and he's got a couple more planned about this subject for later release.

He's improved his youtube channel also, btw, so it's easier to follow the sequence of video's. http://www.youtube.com/playlist?list=PL ... vDCIcEPxUn

PS: A lot of folks I've talked with about this sort of thing respond with a: "Well, I'm never gonna shoot further than 100 (or 200, etc. ) yds, so I don't see any point in learning this stuff". Personally, I think that's a poor attitude to take, but to each his own. Imho such folks will never be more than mediocre shooters, and maybe mediocre in other things as well.

Btw, 1.2 - 0.8Mach is approx. 1305fps to 870fps at std atmosphere. Something to think about when buying/comparing ammo.

 

[John A.]

I have watched a few of those videos and they've been very good in my opinion.

I have not watched all of them, but he has a very down to earth way to explain things, which I respect and makes him easy to listen to. Matter of fact, I watched another video of his of a benelli and saiga shotgun in freezing temperatures just last night.

I personally like to learn as much as I can of what I enjoy and how things work.

If there is ever a day where I cannot learn something new, will probably be the day I just walk away.

This is one specific video that he did that I thought was pretty good that also gets into some of what you're discussing above:

[youtube]http://www.youtube.com/watch?v=J1h2XXXI0Ec[/youtube]

 

[GunnyGene]

That is a good one, John, that is applicable to every rifle shooter. Been awhile since I heard anyone mention dust signature.

 

[John A.]

Reducing dust signature is one of the driving reasons why the military switched from A1 to A2 flash hiders.

That, and directing some gas upwards acts as sort of a muzzle brake.