Fleet yaw

[TiroFijo]

All the studies I've seen show that initial yaw angle quickly reduce to very modest values (3º or less) at 25+ m, see for example:

http://www.springerlink.com/content/t88w048366582508/

When discussing the M193/M855 rounds (perhaps old 7.62 NATO german ammo and others too), and the "fleet yaw" effect that makes some weapons fragment the same ammunition more dramatically (early bullet turn on impact), can we assume this difference is noticed only at very close ranges?

Traditionally all firearm/ammo makers try to have the smallest initial yaw angle as possible to increase accuracy. In CQB weapons, is it possible to increase this initial yaw simply introducing small imperfections on the muzzle crown? The effect on accuracy should be very minor, specially at short range.

[DocGKR]

"In CQB weapons, is it possible to increase this initial yaw simply introducing small imperfections on the muzzle crown?"

Yes, the yaw angle can be significantly increased, but accuracy does suffer rather dramatically--like not being able to hit the target even at ranges under 100 meters. In addition, recall that Fleet Yaw and AOA describe a cycle, where say at 4 meters the projectile is at 1 degree, at 4.5 meters 6 degrees, at 5 meters back to 1 degree, etc... thus leading to inconsistencies in terminal performance.

It is much easier to select projectiles that do not exhibit AOA and Fleet Yaw issues.

[TiroFijo]

Thanks a lot, Doc

Yes, I see the "small muzzle crown imperfections" thing as easy to overdo... and angle of impact will be random as you point out.

Can we assume that these fleet yaw differences go away at 25+ m?

[Failure2Stop]

Thanks a lot, Doc

Yes, I see the "small muzzle crown imperfections" thing as easy to overdo... and angle of impact will be random as you point out.

Can we assume that these fleet yaw differences go away at 25+ m?

It's not a matter of "overdo", its a matter of "unnecessary" and "detrimental". Get a good cartridge and there are less things to go wrong.

They do not go away past 25m. I don't know if there are videos available on the 'net, but there are some very compelling vids of 300m impacts with varying amounts of angle of incidence.

Trying to develop a method to ensure high yaw during impact, or the quest to increase angle of incidence as a method of improving terminal performance is a dead-end. The goal of ensuring acceptable performance without reliance on angle of impact is the way ahead. I know it's hard to do, but trust me on this one.

[TiroFijo]

f2s, this is more of a conceptual question... no doubt it would be much better to choose better ammunition and not worry about the angle of attack.

I'm an engineer and sport/long range shooter and come from an "accuracy first" background, so I kind of understand the desire to keep on target

I still don't understand why the AOA issue does not go away with range, all technical papers (like the ones I posted) that I've read state that normally the initial cycle gets smaller very fast if the twist rate is adecuate for stabilization. There must be other issues at play.

[DocGKR]

AOA and Fleet yaw generally do decrease over distance. For example, a projectile that has a 3 degree yaw at 0.5 meters will be half that by 25 meters, and down to 0.1 degrees by 100 meters.

[Failure2Stop]

As DocGKR points out, they decrease (provided that the barrel provides sufficient gyroscopic stability), but they do not "go away". My point was not that they retain the same variation through their trajectory, but rather that it can and does show up at longer distances in individual cases. I am not sure if the percentage of this occurence is sufficient to include it into the "fleet" yaw category.

ETA- To be clear, I am not disagreeing with Doc, just clarifying my point.

[TiroFijo]

f2s, as I understand it, it should go away in most cases...

A small AOA will not cause a large dispersion in neck lenght/fgramentation statistic data.

All bullets are different, these are some examples of the yawing motion up to 8000 calibers (aprox. 45 m).

armor piercing 5.56 , the yawing motion dampens kickly:
http://www.nennstiel-ruprecht.de/bullfly/fig18.htm

M193, in this particular case (probably not always) the yawing motion does not go away:
http://www.nennstiel-ruprecht.de/bullfly/fig17.htm

russian M74 5.45x39, dampens well:
http://www.nennstiel-ruprecht.de/bullfly/fig19.htm

M80 7.62 NATO, now this dampens very quickly:
http://www.nennstiel-ruprecht.de/bullfly/fig21.htm

[Failure2Stop]

Yes, those graphs are fairly common knowledge, but they only show the close range precession. Precession can come back, the distance at which the precession opens back up varies due to bullet and stability factors, but is one of the problems with small calibers and long range performance.

[TiroFijo]

I know about long range precession, but I think for the purposes of this discussion only close range precession is important, because the AOA influences how early the bullet will turn inside the body but the bullet breakup/fragmentation depends on high impact velocity , found only at close range or up to 200 m depending on the load and barrel lenght.