Whats the practical purpose of 855?

[kx592]

Well was just wondering what the actual purpose of this 855 ammo is for 5.56? Regular 55gr cheapo ammo punches clean through 1/4 steel plates, so whats this 855 going to do?

[MTT TL]

You have already identified the problem.

[Daekar]

My understanding is that 855 is designed with a steel penetrator and is intended to be a multi-functional combat round. Out of a full-sized M16, it will yaw and possibly fragment on impact with a soft target, causing multiple wound channels while the penetrator provides additional, well, penetration.

It has been criticized for inconsistent performance on soft targets, particularly at ranges beyond 200m out of the M16. Of course, the military brought even more of this problem on itself by adopting the M4 carbine, which reportedly has starts to have fragmentation issues at distances beyond even 50m thanks to the reduced muzzle velocity from the 14.5" barrel.

The M855A1 is a new version, which I haven't seen available to consumers yet, that is a solid copper bullet with a separate (that is, it's not covered by the jacket) steel penetrator of larger size. The claim is that it penetrates better than 7.62x51 ball, fragments more reliably (especially out of M4 carbines), has a higher muzzle velocity, and is pretty much better in every way. I heard that it will also do dishes, but haven't seen any graphs on that yet.

The issue here, of course, is that the military must have a single type of ammo that does everything. As you might have noticed when reading about traditional types of ammo, that's usually not how it works - you have ammo that does well in soft targets, and ammo that penetrates really well, not both. The fact that they've got ammo that works as well as it does at both roles is really pretty great, even with the performance complaints that M855 has suffered under. It's my belief that if they hadn't switched to M4s, they wouldn't have to change ammo, but hey, that's just an opinion. I just think that poodleshooters should have long barrels and fast ammo.

[ndking1126]

http://www.army.mil/article/48657/ has this quote:

The M855A1 is not yaw-dependent. Like any other bullet, it "wobbles" along its trajectory. However, the EPR provides the same effects when striking its target, regardless of the angle of yaw. This means the EPR provides the same desired effects every time, whether in close combat situations or longer engagements. In fact, the U.S. Army Research Laboratory (ARL) verified through live-fire tests against soft targets that, on average, the M855A1 surpassed the M80 7.62mm round. The 7.62mm, although a larger caliber, suffers from the same consistency issue as the M855, but to a higher degree.

That article has other great info too.

[44 AMP]

The steel cored "penetrator" ammo (M855) was developed to counter the body armor being brought into service by Combloc troops in the late 70s. The standard M193 55gr ball was thought to be insufficient against armored troops.

Not sure who figured all this out, we weren't actaully shooting at Russians or East Germans in those days.

Apparently now days, because of the lower velocity from M4 carbines, the 855 isn't doing such a great job at exdtended ranges as is desired, so we are getting another change to the 855A1.

"yaw" is a fine term, describing the "wobble" of a bullet in flight. But, the yaw in flight is very small (otherwise you lose accuracy). Yaw is also used to describe the "tumble" of a bullet as it passes through flesh. And here is where confusion results. ALL pointed bullets will "tumble" as they penetrate soft targets. The shape of the bullet means that it will turn base first. What varies is the distance through soft target needed for the bullet to do this.

Typical .30 caliber bullet turn in around 14" of penetration. This usually means they have exited the enemy before having completely flipped. The small .22 bullets do it in much less tissue travel, and that is what improves their effectivenss.

The M855 bullets are intended to turn (yaw), and actually break apart at the cannelure inside tissue, doing the most damage practical. BUT, this is depenent on the velocity they impact with. Fired from carbine barrels, the slower speed at longer ranges means the bullets don't perform as well as intended, reducing combat effectivness.

Hopefully the new rounds will correct this.

[Bartholomew Roberts]

When NATO originally standardized on a caliber, the United States basically forced 7.62x51mm down the throats of the other NATO members, and then just a few years later, the U.S. abandoned that caliber for the 5.56x45 M16 as a general issue infantry rifle.

By the mid-1980s, it had become clear that the U.S. wasn't going back to 7.62x51, so NATO decided to standardize on 5.56mm. One of the issues that 5.56x45 had always had trouble with was being able to penetrate 10ga mild rolled steel (and old M1 steel helmet) at distances over 500m. The NATO requirement called for this ability at 600m. FN managed to come up with a 62gr 5.56mm variant using a 4.7gr steel penetrator that did this reliably they called "SS109." This was ultimately what NATO adopted, though each country has slightly different standards for the so-called standardized ammo. The U.S. version is M855.

With M80 (7.62x51), M193 and M855 ball, the bullet basically traces very, very tiny circles in the air as it flies along its trajectory. Closer to the muzzle the circles start out a bit bigger and then settle down as the bullet gains stability. As 44AMP pointed out, all spitzer shape bullets want to tumble when they hit flesh, it is just a question of when this happens. The momentum of the bullet and the angle of attack of the bullet (where it is at on the tiny circle it is tracing) affect this, but the effect is more dramatic in the smaller 5.56x45 caliber because it has less mass and slows down/yaws faster. As a general rule, M193 or M855 will yaw within about 4-5" of ballistics gel about 70% of the time. 15% of the time, they will yaw earlier and 15% of the time, they won't yaw until after 7" or more of gel.

Being smaller and travelling faster, M193 and M855 both can also be stressed enough to break apart at the cannelure when it yaws (generally above 2700fps, though it can happen at lower speeds). When this happens, the tiny led fragments poke tiny little holes all through the stretched out tissue in the temporary cavity. The combination of stretching and tiny holes causes tissue to detach and creates bigger wound cavities than would be caused just by bullet yaw alone.

However, since where/when the bullet yaws is dependent on the mostly random factor of where the bullet is in its angle of attack (and this randomness gets worse under 50m), this is not considered a desirable trait.

The new M855A1, while it has its own issues, is apparently not dependent on this angle of attack. It yaws and tumbles at a consistent depth every time regardless of its angle of attack. On the other hand, the mostly copper bullet doesn't seem to fragment quite as dramatically as earlier M193 and M855. So while it has better barrier penetration, it tends to create less dramatic wound tracks.*

*I'm not a ballistics expert by any means; but I've been reading this stuff for about 12 years now and have read everything from the original Project SALVO studies up to Fackler, IWBA, etc. This is just a synopsis of what I've read as I remember it. Use at your own risk. Offer not valid in all 50 states.

[Gehrhard]

Note an intent of the 62 grain round was to provide longer range accuracy and European, down range, battelfield effectiveness that the 55 grain would lack.
Note further that the 855 US cartridge is hotter than the Allies' rounds, i.e. SS109.
Note further still that civilians are not shooting 14-1/2" barreled carbines -- we have 16" guns. And better true mid-length gas systems and 18" barrels are available too.

These are a great combination with that 855 and the semi-automatic civilian carbine and full length rifles is probably a better gun than the military's M4 is a machine gun with that cartridge.