Weekly DTIC: The Fleet Yaw Problem, and Improving Rifle Effectiveness

Nathaniel F
by Nathaniel F

Stepping out of the chronology that the past few Weekly DTIC entries have taken, today we’ll be examining two much more modern pieces of research, which help explain some of the phenomena observed by end-users when firing their weapons in anger. The first document is Small Caliber Lethality: 5.56mm Performance in Close Quarters Battle, by Majors Glenn Dean and David LaFontaine. This magazine article, originally published in September 2006 in Infantry Magazine, covers the results of Army Research Laboratory studies carried out to help determine the underlying cause of erratic terminal performance from 5.56mm weapons in the field. The second, Small-Caliber Projectile Target Impact Angle Determined from Close Proximity Radiographs, is a technical mate to the first, describing the process eventually used to generate the scientific data necessary for the fleet yaw theory.

The background of why these studies occurred should at this point be familiar to readers of TFB, but bears repeating. 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.

The first article explores this background, and the challenges the investigators had to face in very satisfying detail. 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.

Perhaps even more important than this discovery – in terms of the solutions it informed – was the fact that all projectiles tested, including 5.56mm, 5.45mm, 6.8mm, and 7.62mm projectiles of a wide variety of weights and types of construction, exhibited this flaw. While changing calibers to, for example, the 6.8mm Remington, might increase the energy per shot of service carbines, doing so would not solve the fleet yaw problem on a fundamental level. Further, it was determined that, while no such design currently existed on the commercial market, a projectile in the current 5.56mm chambering could be designed to overcome this effect, one which could yaw and fragment at all angles of attack, ensuring reliable terminal effects. These conclusions led directly to the four current in-service yaw-independent projectiles, M855A1, M80A1, Mk. 318, and Mk. 319.

Nathaniel F
Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. He can be reached via email at nathaniel.f@staff.thefirearmblog.com.

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  • Bad Penguin Bad Penguin on Jul 30, 2014

    So where is the follow up with showing the flight patterns and ballistics of the new rounds? As far as reports of inconsistent lethality of the M855 round I have to ask why you were surprised. This has been a problem with the 5.56 round from day one. Did anyone bother to test each round with different barrel lengths? Manufacturers? Ammo Manufacturers? Israeli Arms makes about 15% of our rifle ammo and Lake city makes the rest. Which makers ammo performs the best. Looks like too little testing was done to write a real article.
    BTW I have heard anecdotal reports of the M855A1 rounds falling apart.

    • Nathaniel F. Nathaniel F. on Jul 31, 2014

      @Bad Penguin Really? Initial reports of the .223 round used in Indochina showed it performing better than .30-06.

  • Pete Pete on Jul 31, 2014

    I think the germans had a solution on Sturmgewehr 44 where they put an attachment on the barrel which made the bullet leave the barrel in an angle. This seems not to have been very common from what I have read.

    • Nathaniel F. Nathaniel F. on Jul 31, 2014

      @Pete Those were for shooting out of ports on AFVs and did not work very well at that. They had nothing to do with improving the terminal effectiveness of the projectiles.