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Tuesday, July 29, 2014

The Fleet Yaw Problem

The Firearms Blog has an article discussing the problem of yaw and FMJ bullet effectiveness, referencing two studies on the topic: Small Caliber Lethality: 5.56mm Performance in Close Quarters Battle, by Majors Glenn Dean and David LaFontaine, and Small-Caliber Projectile Target Impact Angle Determined from Close Proximity Radiographs. As TFB notes:
Essentially, recent infantry deployments resulted in reports of inadequate effectiveness from 5.56mm weapons – but, strangely, the reports were not uniform. Some units described their weapons as being highly effective, but others report having to make multiple hits on targets to have the desired effect. This was largely unexpected - the M855 5.56mm round produces very high muzzle energy for its caliber, and the projectile is designed to yaw violently – if not fragment – depositing its energy rapidly and effecting a stop. At short distances, it should have been very effective. 
... What resulted from their investigation was a landmark discovery in terminal effectiveness science: Bullets – all bullets, not just .22 caliber ones – experience a period of very violent yaw and turbulence when they exit the muzzle, causing their angle of attack relative to their flight path – that is how “straight” the bullet is in flight – to vary wildly. Within 50m, they found, two bullets fired from the same gun, at essentially the same time, might impact a target at two completely different angles. A bullet impacting head on into gelatin would stay stable for much longer than one impacting at a high angle, and would deposit its energy much later. This explained the problems some users – but not others – were having with their weapons. In some instances, the FMJ projectiles would hit the target at a desirable high angle of attack, tumble and fragment within a short distance, and reliably stop the target, while in others, the same type of projectile would hit at a flat angle, and might not yaw for many inches. 
Read the whole thing.

4 comments:

  1. I find it ludicrous that a non-signatory to the 1899 Hague Agreements on use of hollow-point ammunition, but an adherent to the Laws of War, Humanitarian treaties, and Nuremberg canons virtue signals by using jacketed bullets, and then invests time and research into ways to make them tumble and fragment in order to achieve the level of damage of a hollowpoint. "I don't smoke, but I seek out those who do so I can breathe the air around them." I feel like the world has become one large insane asylum.

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    1. There are other good reasons to use FMJ in a military setting, such as reliable feeding in a fully automatic weapon and resistance to deformation of the bullet tip in handling and storage.

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    2. Just came back to this in a review, and saw your comment. Most definitely, there are reasons for use of FMJ, not the least of which is barrier penetration - although the 855 is marginal compared to heavier rounds, as we know. My comment related more to the hypocrisy of eschewing expanding bullets for "adherence to (Hague) convention" - presumably to minimize lethality, motivated by the Dum-dum Arsenal experiments and the German protests - and then to do our damnedest to make those non-expanding bullets as lethal as possible. I am not lobbying on behalf of use of FMJ on "humanitarian" grounds - shooting another person is not humanitarian in any sense - but rather on admitting that the job of a weapon is to stop an adversary, now, and excluding effective projectiles from use in that circumstance, on such "humanitarian" grounds is absurd.

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    3. @ Steele: I understand and agree with your point. It was hypocritical even at the time of the Hague convention since exploding shells and shrapnel are certainly more inhumane than a Dum-Dum bullet.

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