Energy of SS109 at 600m

B

Bartholomew Roberts

Moderator
I had been reading of some people claiming regular 600m shots with AR15s over at AR15.com.

This got to me wondering exactly how much energy would even be left on an SS109/M855 round at 600m. I figured if anybody would know the answer to this question, this would be the place to ask.
 
M855 is able to penetrate the U.S. M1 steel helmet at 600m. That was the criteria for development of the cartridge.

That being said, the ability to penetrate the M1 steel helmet at 600m doesn't necessarily make the round suitable for defensive use or medium to large game at that range.

The current 5.56mm military cartridges have their best terminal effects at velocities above 2500 feet per second. At 2500 fps and higher the round breaks at the cannulure and fragments. The rounds fragment most reliablby above 2700 fps, but tests done by Dr. Martin Fackler of the Army's Wound Ballistic Lab placed 2500 fps as the bottom threshold for this effect. These fragments create their own permanent wound channels causing greater damage then the bullet would if it didn't break up.

Yes the bullet tumbles when it hits, but all spitzer type bullets will do this if sufficiently disturbed. It's just basic physics, most of the weight is in the back of the bullet and when it hits something, the weight tends to move in the direction of travel.

M855 is only at optimum velocity for about 125m out of a 14.5 inch M4 carbine, and a little more then 200m out of a 20" M16A2.

So yes the round will penetrate a steel helmet at 600m, but it won't be moving fast enough to fragment and create the massive wounds it does at the higher velocities.

Jeff
 
According to my handy-dandy Sierra loading data book, a .22 bullet of 63 grains (sorry, semi-pointed flat base is all they listed), leaving the muzzle at 3,000 ft/sec will be at
1,236 ft/sec at 600 yards, with kinetic energy of 214 ft/lbs. A pointed boat tail will maybe be a couple of hundred ft/sec faster...You're in the .22 rimfire vicinity.

To actually penetrate a helmet would require a fairly direct hit; the bullet would easily glance off if there is much of an angle.

Art
 
So when the SS109 drops below about 2000ft/sec its "out of gas" pun intended. Since I am at work would someone look it up and see at what range this occurance happens.

[Edited by Alan B on 04-20-2001 at 01:49 PM]
 
I don't have access to ballistic tables at this time, but I did perform an experiment last year with Israeli made SS109 green tip ammo. The weapon was a 16" CAR15 scoped with a 4X ACOG. I was firing at heavy steel plates from 100 to 600 yards. At 600 yards 223 ammo loaded with Nosler Ballistic Tip bullets barely scratched the paint on the gongs. The SS109 was something else. It left the steel penetrator fully imbeded into the steel plate just like a nail in a board. I was unable to pull the things out! I was surprised. An old GI steel pot helmet would have been no problem to blow through. If I hadn't seen it, I wouldn't have believed it. Effective wounds at 600M? I don't know, but my gut says your steel pot is not going to save you.
 
If someone's 600 yards away and you hit them directly with one, they will be hurting and you can probably outrun them ;)

That energy level puts it more in the league of a .22 mag rifle point blank. I don't kow about you, but a .22 mag rifle point blank is going to sure as heck slow me down.
 
The SS109/M855 has very good penetration ability, roughly the same as 7.62 AP (difference is insignificant).

Source: USMC Pub "Machineguns and Machinegun Gunnery."

On steel pots - we don't wear them any more, but I suppose the enemy still does. In any case, kevlar or steel, they're not intended to be bulletproof, just protect against fragments. That's why the majority of the protection is on the top and sides, and the main reason why direct action guys like Delta and SEALs don't bother to wear them (they're getting shot at, not shelled in a trench).

Semper fi.

Bruegger out.
 
Let's not get too hung up on the obsolete steel pot helmet. At 600 yards the SS109 penetrator is capable of poking a hole in damn near anything, including you. That's gotta hurt.
 
Bruegger
at 500m a 7.62 Nato AP is supposed to penetrate 1/2 inch of homogneous armor plate.

so in reference to you comment huh??
 
I never meant to imply the bullets would bounce off your jacket

Never once did I say the bullets had no effect at 600m. I said their wounding effect wasn't optimal at that range.

I read somewhere once that more lives, animal and human, were taken with .22LR then any other cartridge. This shouldn't be taken to mean that .22LR is the optimum cartridge for all uses.

Naturally any bullet that will penetrate the old steel pot at 600m will certainly penetrate your body and cause a serious wound. But the M855 won't break at the cannulure and fragment at that range, which is what makes it so much more effective then many other rounds when it hits at it's optimum velocity.

My point was that if you are shooting at anything but paper, gongs or silhouttes at that range, you might want to consider a round that had better terminal effects that far down range.

Jeff
 
Alan B asked: "at 500m a 7.62 Nato AP is supposed to penetrate 1/2 inch of homogneous armor plate. so in reference to you comment huh??"

All I can say is check the pub.

My point was that the general assumption that 7.62 massively out-penetrates the 5.56 is not true, at least at close range.

According to USMC publication Machineguns & Machinegun Gunnery, the SS109/M855 penetrates 12mm at of armor at 50 meters and 9.9mm at 150m. I would guess 11mm at 100m.

Doesn't sound too far from 1/2" (=12.5mm) at 100m to me! But I'm just a dumb Marine who used to run a MG platoon, so what do I know?

The M995 made by Bofors is a genuine-article 5.56mm AP round, and is probably a fairer round to compare to the 7.62 AP round. It penetrates 1/2" at 100m, which is the same as the black tip 7.62.

Semper fi.

Bruegger out.
 
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