All M193 Is Not M193
BY Herschel Smith
2 years, 8 months ago
Zero with the best ammunition you will shoot, and use that for self defense. Otherwise, I agree with him. Buy what you want, but don’t expect the same performance.
This is also a reminder that shortened barrel lengths (seemingly all the rage now) create this same problem.
On April 26, 2022 at 1:10 am, Georgiaboy61 said:
As the video notes, 55-grain M193 FMJ/Ball ammunition was intended to be used from an AR15/M16 with a 20-inch barrel.
The U.S. Army’s “light rifle” competition was instigated by U.S. Army General Willard Wyman, the commanding general of CONARC, in the mid-1950s. Since the specification set forth by Wyman’s command called for a .224-caliber bullet and also wounding potential equivalent or superior to the M-1 Carbine, that’s what Eugene Stoner and his team used as their starting point.
Stoner later explained that in order to get a projectile as light as 55-grains to do the job, he exploited the known dynamic instability of lightweight, high-velocity projectiles moving at high speeds. Specifically, their propensity to yaw in flight and then “swap ends” (tumble) when encountering a target.
As an aside, it is important to note that this propensity has been misinterpreted over the years to mean that the projectile (bullet) itself tumbles while in flight. This is incorrect. The whole point of rifling a barrel is to spin-stabilize the projectile by spinning it at very high rpm. Rather, the yawing and subsequent tumbling occur when the bullet encounters a target such as living tissue.
Usually, “keyholing” on a paper target is evidence of dynamic instability and an insufficiently rapid rate of twist to stabilize the projectile.
Stoner’s team increased the wounding potential of the 55-grain bullet by including a cannelure or crimping groove in the design, at which the bullets would often fracture or shatter if moving at sufficiently high MV. Instead of a caliber-sized hole, multiple high-velocity wound tracks would be created, thereby increasing the potential lethality of the projectile.
A modern pointed (spitzer) rifle bullet is tail-heavy anyway, since the center of gravity is usually aft of the midpoint of the projectile. It is kept in its proper nose-first orientation by the high rate of spin imparted by the rifling and the velocity of the shot itself. This orientation breaks down only when the bullet has traveled far-enough to shed much of its velocity and rate of spin, or when the projectile encounters a target of some kind which slows it down dramatically. It is then that the projectile will want to “swap ends” into a tail-first orientation, possibly shattering if velocity is still high-enough.
After-action reports coming out of Vietnam painted an inconsistent picture initially. Some troops reported stunningly-effective terminal performance and combat effectiveness, whereas others reported indifferent terminal performance and a failure of M193 to put down enemy “tangos” hit center-mass. It is now thought that these reports merely reflected the somewhat idiosyncratic characteristics of the M193 round, its dependence upon certain conditions for optimal effectiveness in combat.
These findings were later confirmed by rigorously-controlled studies done at Crane Naval Special Warfare Center and elsewhere, but at the time, they sparked an intense controversy within military circles about the relative worth of the M-16 and its 5.56x45mm ammunition which has still not abated today.
The new 62-grain “green-tip” M855, the NATO standard going forward from the 1980s, intensified this debate, since its performance in battle was, if anything, less-consistent than M193 before it. Again, as Crane and others would eventually prove, due to inconsistent terminal performance by the bullet itself.
NATO – in seeking to “improve” the terminal performance of M193 against mild steel sheet metal such as that found in a standard Warsaw Pact helmet – ended up degrading the fragmentation potential of the projectile at close-to-medium ranges. Instead of yawing and fragmenting as intended, the new steel penetrator embedded into the forward part of the bullet tended to cause “through and throughs” or “ice-picking” of targets.
In other words, the shots were passing through enemy personnel without taking them out of the fight, sometimes after multiple center-mass hits. This lack of consistency of performance became public knowledge after the publication of “Blackhawk Down,” Mark Bowden’s superb account of the 1993 action in Mogadishu. Delta Force operators and Rangers were scoring multiple center-mass hits against Somali militiamen – yet seeing them remain in the fight.
In the latter half of the 1990s and into the global war on terror era, the inconsistencies of M193 and M855 are part of what drove the intense amount of R&D into finding newer and better solutions for America’s soldiers. Specifically, our finest fighters wanted ammunition which would work better out of short-barreled, often-suppressed SBRs and carbines, and not just full-length 18-20″ rifle barrels, and the troops also wanted better performance against barriers and at ranges past the optimum for the older M193 and M855 projectiles.
OTM (open-tip match) loads supplied the answer for the former, since they fragment reliably at a much wider range of MV values (including subsonic ones) than the old M193 and M855 loads, and bonded core and/or solid-shot projectiles provided the needed performance against automotive glass and sheet metal that the older bullet designs were not giving.
Eugene Stoner’s design is now arguably (depending on how one parses the data) the longest-serving American service rifle, and has matured into an effective weapons system – but like any firearm, the ammunition chosen for it matters a great deal in what sort of results the user can expect in the field.
On April 26, 2022 at 5:43 pm, Silence DoGood said:
“…This is also a reminder that shortened barrel lengths (seemingly all the rage now) create this same problem.”
It bears mention that the SF were the driving force behind the creation of the 6.8 SPC because they are quite fond of 10 & 11-inch M4s/HK416s but such short barrels weren’t producing terminal performance adequate to their needs. The 6.8 was the remedy to that problem. I doubt there would be so many of these AR-15 “pistols” being built/bought if more shooters were aware of this factoid.