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.