7.62 being replaced by 5.56?

Originally posted by spock:
In penetration tests on steel plates, there is no real noticable difference.

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Ummmmm.....I'd really have to see those test results. One of the 7.62's biggest advantages is superior penetration. What is cover for 5.56 is only concealment for 7.62. Trees, bricks, concrete, steel plate are all penetrated FAR better by 7.62 in my humble experience.

The best story I have is from when I left two friends "new" to shooting unsupervised after they demonstrated they could safely operate my HK91 and HK93. I left them to shoot at paper targets and was loading mags for my HK53 (yeah, I'm a HK fan) when I began to hear "BANGTINK" instead of just "BANG". Bored with paper targets, they had transitioned to the steel reactives. Screaming "CEASE FIRE!!!", I range walked over to them and informed them that we do not shoot the pistol targets with rifles.

Expecting the worst, I went down and inspected the plates. The 5.56 hits left nice splatter marks but did not even dent the plates. There were several very neat 7.62 holes completely through the plates.

Man, those things are expensive!

But, in no way, shape, or form does a 5.56 have anything close to the penetrative power of a 7.62.



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Some say he is a Zen master....
Others say he is a ****head.
-John Overton

If I remember my physics correctly, penetration is a function of momentum. It is the struck body's inability to overcome a projectile's momentum that causes it to be penetrated.

Momentum is the product of the mass of a body and its velocity.

7.62X51 vs. 5.56X45, the 5.56 has a roughly 20% edge in velocity (at the muzzle, but this advantage decreases steeply with distance), but the 7.62 always has a 267% edge in mass (55 gr. vs 147 gr.).

The 7.62 always has an enormously greater amount of momentum, and thus penetration. That is why you can shoot through larger trees and thicker armor with a 7.62.

Now, of course, other factors such as relative hardnesses and densities of the projectile and body come into play, but the 7.62 will always have an insurmountable momentum advantage over the 5.56.

Any ex-physics professors out there?

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Some say he is a Zen master....
Others say he is a ****head.
-John Overton

Think of it like this...

Two tractor trailers. Exactly the same, except one has an empty trailer and the other has a trailer full of depleted uranium. On the green light, both accelerate to the exact same speed and maintain the speed until they impact a reinforced concrete wall.

They will both impact the wall at the same time, but the one with the heavy trailer is going to do much more damage than the one with the empty trailer due to momentum. Mass times velocity.

Of course, in this example, we have no deceleration of the trucks as we would with bullets over distance. This is where BC comes into play. The bullets are slowed by air friction. Less air friction, less deceleration over distance. Higher BC, lower air friction.

As spock said, if you had two bullets leaving the barrel at the exact same time and with exactly the same velocities, the bullet with the higher BC would arrive first, with the advantage increasing over distance.

But, if the bullets have different masses, then the heavier bullet, though probably slower and with a lower BC, will retain its velocity better over long distances, say 400-500 yards or more, due to its momentum. If the drivers of those two trucks simultaneously let off the gas (letting air friction and gravity do its work), the heavier truck will travel farther because it has more momentum.

Like I said, any ex-physics professors out there?

[EDIT] Ooops, I forgot. If you want a graphic example of what I'm talking about, go here and play with the "Define your own bullet" button. Experiment with velocities, masses and BC's. It makes it pretty clear:
http://www.norma.cc/htm_files/javapagee.htm
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Some say he is a Zen master....
Others say he is a ****head.
-John Overton



[This message has been edited by Villuj_idiot (edited 10-27-2001).]

Originally posted by RikWriter:
The advantages of 223 over 308 are clear enough to anyone that has had to hump through the boonies for any length of time, and abundantly clear to anyone who's ever seen the rounds used against living tissue.

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I have some small experience in that area. No doubt, at close engagement ranges, there are some horrendous exit wounds. I never cut anybody open to see what the insides looked like (at least what of their insides I couldn't already see), but I'll bet there was a lot of damage in there.

I have also seen first hand the truth of the pat saying, ".223 cover is .308 concealment". The 7.62 has better penetration of armor and the normal equipment soldiers have clanging around them. The 7.62 will go through that 1' diameter tree and kill you. And if the first one doesn't make it through, one 20-round mag and the tree is cut down, or close.

Personally, for serious antisocial events, I want a larger, heavier round to expend. The only time I have ever preferred having a 5.56 over a 7.62 was after having to hump a heavy rifle and heavier ammo for a day or so. But that was purely for comfort reasons.
And comfort reasons usually have little to do with effectiveness in a fight.

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Some say he is a Zen master....
Others say he is a ****head.
-John Overton