In response to the ongoing dustup over M855 ammunition, Ian and Karl of InRange TV have done a short video explaining some basics about the round, and its capabilities. As host website Full30 does not allow videos to be embedded on other websites, readers will have to follow the hyperlink to watch the video.
The basic points that M855 is neither a magical armor penetrator, nor is exceptionally effective from a terminal ballistics standpoint – and a brief demonstration of the round’s limited accuracy potential are all well-made, but there are a few statements that Ian makes in the video that I feel either need clarification or that are a little too strongly argued.
The first is that M855 was designed specifically to penetrate a Russian helmet at 600 meters, and that this was an unrealistic target for soldiers armed with M16’s – this is true, but a little misleading. Fabrique Nationale’s SS109 – the parent type of M855 – was intended to provide an adequate ball round that could also be used in the new squad-level automatic rifle – the FN Minimi which would enter US service as the M249 SAW, while retaining the positive characteristics of M193. The simplest way to accomplish this was simply to lengthen the bullet jacket, change the tangent ogive to a secant ogive with a much finer meplat (both improving the form factor of the projectile and thus its ballistic coefficient), and to add a small conical steel insert to the front. This insert wasn’t a true armor penetrating core, but was simply designed to breech the helmet, allowing the rest of the bullet mass through and causing a fatality. While aiming for individual helmets was totally unrealistic – even for the fully automatic M249 SAW, a round that couldn’t penetrate a standard enemy helmet and produce a casualty at what was supposed to be its effective range would not be suitable for military service. So, whatever the consequences, SS109 won the competition and it was assumed the positive characteristics of M193 would be retained. The takeaway here should be that while the deciding characteristic of what would become 5.56×45 NATO was how well it penetrated a Soviet helmet at 600m, it is not a specialized armor penetrator like rounds such as the 5.8x42mm DBP-10, 5.45x39mm 7N22, or .30 M2 AP. However good or bad the design, it was intended as a general-purpose round, suitable for both soft and hard targets.
The requirement for a 1:7 twist is our second clarification: This was not necessitated by the 62gr SS109/M855 bullet, but rather by the much, much longer 64gr M856 tracer. The tracer projectile is longer even than M855A1 or Mk. 262, which is why a twist rate change is not necessary for use of either of those rounds. The M855 bullet itself can be stabilized sufficiently under temperate conditions by twist rates as relaxed as 1:10.
Ian makes a few statements regarding M855’s lethality that I think are also worth addressing. The below quote is taken from the video’s description:
Frankly, M855 is probably the worst military-issue 5.56mm ball ammo ever made.
The original 55 grain M193 ball had a tendency to tumble in the body and make effective wounds. The new Mk262 77 grain ball also destabilizes quickly, and has much better long-range energy retention than the M193. The M855 was designed to poke holes in Russian helmets in the Fulda Gap, and offers poor wounding ability and poor accuracy.
The initial statement in particular ignores the initial ammunition issued under the designation “M193”, before case hardness specifications were laid down. The lack of case hardness specifications resulted in problematic extraction, exacerbating an already bad situation. Further, M193 was never held to a high standard for accuracy, either, so making that comparison is a little uneven.
In the video, Ian says more:
When it comes to ballistic effect, this is an area of significant problem with the 855. Because it was designed to penetrate Russian armor, it doesn’t really do anything when it hits a medium like a human. What you get is frankly what happened in Mogadishu, if you watch Black Hawk Down you saw the effect; it pokes little holes, it does not destabilize when it goes through a person. So as a result it doesn’t have a whole lot of terminal effect.
To say that it “doesn’t destabilize” when it hits a person is incorrect. What needs to be understood is that the results of gunshots even under similar conditions are highly variable. M855 certainly has the capability to make grievous wounds through fragmentation – it is, after all a fairly close relative to M193, sharing its boattail, materials, jacket thickness, and cannelure. So where does the reputation for its poor terminal effect come from; what’s the science behind through-and-through wounds, and is M855 especially prone to that outcome relative to other 5.56mm FMJ types?
A complete answer to this question is beyond my level of expertise, but there are a couple possibilities. First, the fleet yaw problem necessarily means M855 will have highly variable results at close range. Beyond close range, the 1:7 twist rate could be causing a reduced angle of precession, and therefore possibly a lower likelihood of early yaw and fragmentation.
One other possibility is that the steel insert is supporting the nose of the jacket enough to preclude the possibility for yaw-less fragmentation. I have no direct evidence that M193 is capable of head-on fragmentation, but there are some supporting anecdotes of early 5.56mm impacts on extremities that resulted in grievous wounds, which could have been caused by yaw-less fragmentation. If it were proven that M193 was capable of yaw-less fragmentation, and that the steel insert in M855 reinforced the jacket enough to preclude that possibility, that could be an explanation for M855’s perceived low effectiveness. However, further studies of the probabilities of different outcomes for both M855 and M193 strikes would need to be conducted to fully confirm this theory.
What is clear is that while it’s not a certainty that M855 will produce through-and-through wounds – which is no help to those who have had the round fail on them in combat, it is true that the round has been found lacking in Army use. This desire for a more effective round led directly to the development of both the Mk. 318 and M855A1 rounds.