Are M855 Rounds Good For Anything?

[Coal Dragger]

Been there, done that. Actually I usually had the SAW, which was worse. Plus, I am tall enough that I couldn't sit up straight with my k-pot on, esp with the PVS-14 attached. I still prefer the M16A4. It's not as fast in and out of vehicles or through doorways, but that is only a part of infantry duty. For everything else, the M16 is superior, plus, it is a more durable, more reliable, smoother running machine.

I have come to prefer an 18" bbl with rifle length gas and a collapsible M4 style butt stock. Best of both worlds, doesn't give up much velocity to the 20" bbl, and can be made compact enough to manage in the confines of a cehicle. Put a Nightforce NXS 1-4×24 with an FC-3G reticle on top of the rifle and you've got a very versatile rig.

I ran this set up in a Pat McNamara class and feel that at close distances I was in no way hindered compared to 14.5" and 16" guns with red dots, and as distances increased I could turn the optic up to 4× and it would stomp all over the red dot equipped carbines for fast accurate hits at distances greater than 75 yards or so.

I just wish Nightforce would make a 1-8×30 with day light bright illumination on the center dot, use the FC-3G reticle on 2nd focal plane, and keep optic weight around the 1-1.5lb mark.

 

[benEzra]

But we know that a 62 grain bullet out of an AR15 cannot attain the same MV as a 55 grain bullet out of the same rifle. So I think the question should be, if a 55 grain bullet and a 62 grain bullet are loaded to their highest MV, which will penetrate better?

The tests I've seen show an M193 (probably just barely) penetrating AR500 steel, and M855 (more likely to penetrate than a simple jacketed lead bullet) bouncing off.

This.

M193 penetrates slightly better at closer range, due to its higher muzzle velocity. M855 retains its (lower) velocity better, and does undoubtedly penetrate a little better at any given velocity, so past 100 or 200 yards M855 out-penetrates M193. IIRC, the specified adoption criteria for M855 over M193 was penetration of a steel helmet at 600 meters, which low-BC M193 could not reliably do due to velocity shedding.

 

[lysanderxiii]

All that leads me to believe that against steel targets, speed is the main factor in penetration, all other factors equal.

Bold

Hard target penetration depends on three things: 1) striking velocity, 2) mass and 3) construction.

Striking velocity is the speed the bullet has on impact, obviously this depends on the range and the ballistic coefficient, higher BC bullets carry more speed at further ranges.

A 150 gr bullet penetrates more, at the same velocities than a 55 grain bullet.

Construction, M2 Ball and M2 AP have very nearly the same Vm, AP being slightly lower, yet at zero range AP is obviously better.

Which is why DU M829 penetrators go through more armor than DM 53 WC penetrators at all ranges, even though the Vm is the same, approximately 5500 fps.

And, why US battleship rounds out performed Japanese battleship guns for the same striking velocity, our shells had better designed noses.

 

[lysanderxiii]

But we know that a 62 grain bullet out of an AR15 cannot attain the same MV as a 55 grain bullet out of the same rifle. So I think the question should be, if a 55 grain bullet and a 62 grain bullet are loaded to their highest MV, which will penetrate better?

The tests I've seen show an M193 (probably just barely) penetrating AR500 steel, and M855 (more likely to penetrate than a simple jacketed lead bullet) bouncing off.

This.

M193 penetrates slightly better at closer range, due to its higher muzzle velocity. M855 retains its (lower) velocity better, and does undoubtedly penetrate a little better at any given velocity, so past 100 or 200 yards M855 out-penetrates M193. IIRC, the specified adoption criteria for M855 over M193 was penetration of a steel helmet at 600 meters, which low-BC M193 could not reliably do due to velocity shedding.

At 50 yards neither will penetrate a 1/2 inch plate.

https://www.youtube.com/watch?v=wcqlvjcQpEY

https://www.youtube.com/watch?v=wb-ClokH0ks

A very close range M855 still does better.

The striking velocity for M855 is about 2400 fps:
https://www.youtube.com/watch?v=x7OeYO-oHGw

The striking velocity for M193 is much higher, around 3340 fps
https://www.youtube.com/watch?v=FfA3Qv9JjBA

(Note: it's the same plate maker....)

 

[strambo]

I've always thought an 18" barrel rifle gas with an A5 stock system would be a perfect blend of range and portability for the Marines. I understand why it isn't worth the hassle...but a mix of M4's and M16A4's with the A5 stock would be a solid compromise and it is all in the system.

I like M855 for general stockpile ammo though M193 is a bit cheaper and works just fine as well.

 

[tark]

The only "green tipped" rounds I fired were 7.62 NATO. Duplex bullets one behind the other. More gimmick than anything else, I think..... Pretty sure they are no longer in the inventory.

 

[benEzra]

A very close range M855 still does better.

The striking velocity for M855 is about 2400 fps:


The striking velocity for M193 is much higher, around 3340 fps

lysanderxiii, those are two very different plates, and two different plate ratings. That first video says it tests an "ultra lightweight" NIJ III plate (thinned down to just meet the NIJ III spec?) and the second video is of a NIJ Level III+ plate, not NIJ III. The NIJ III+ plates like in the second video are specifically designed to stop M855 up to 3100 ft/sec, M193, and 7.62x51mm black tip.

http://www.ar500armor.com/ar500-armor-10-x-12-asc-level-iii-body-armor.html

Here's an apparently less-lightweight NIJ III plate shot by M193 and M855 at the same distance from the same gun; M193 penetrated due to its higher striking velocity, M855 did not.



Generally speaking, it appears that under equal test conditions (same plate rating, same test setup), M193 seems to slightly edge out M855 at close range, at least out of 20" or longer barrels. Out of short barrels, it is possible that M193 would lose more penetrative ability vs. M855, but I haven't seen that test.

I think the moral of this story is that if you are going to bother buying rifle-resistant armor, go with the III+ spec instead of basic III, because armor designed to just barely meet the III spec (slowish 7.62x51mm FMJ) will often fail with either M855 or M193 at close range out of a longish barrel, especially armor styles that are optimized for the lightest possible weight for a given spec. Basic III plates will still protect against longer-range or shorter-barrel shots, but aren't reliable at close range.