7.62 being replaced by 5.56?

Keywords; "good shot placement". Indeed, I have shot rabbits with a .45 - and they didn't stop and die any quicker than hits in the right place with a .22LR.

But what precise shot placement with just about any .22 caliber rifle cartridge and a FMJ bullet can do on deer aside..... if my life is at stake, I know which one I would choose - every time, at any distance

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

Click to expand...

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

I have fired 30-06 WW2 vintage AP and the various 5.56 AP at various thicknesses steel plate. Even allowing a generous difference in velocity between 30-06 and 7.62 NATO I'd bet some good money that 7.62 will outpenetrate 5.56; in any standard FMJ and AP comparison.

Against wood, masonry or any other tactical barriers I agree there is no comparison.

Villuj_idiot,

I used to attend a club where a note was posted swearing cost recovery for the welded repairs to a bunch of pistol plates!

GI-45,

It is a combination of factors; material (bullet) and construction, sectional density, mass, velocity and even such mundane variables as bullet stability. The 5.56 loses velocity fast, and a significant amount is lost from the short 16.5" barrel. As the range increases, the difference in velocity between a 7.62 and a 5.56 rapidly starts to disappear. Penetration of hard tactical barriers will be reduced proportionately.

Spock,

I would compare ball ammo with ball ammo - and AP with AP

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

Originally posted by GI-45:
...I've noticed that 5.56mm has become far more common than 7.62mm....

Click to expand...

Yes it has. And not for the good. Let me respond to a whole bunch of posts instead of one-by-one replies.

The 5.56 is an anemic round. It's adoption has far more to do with what DSK wrote of than any kind of ballistic superiority.

I am in a military reserve component. I also work security for the feds full time. Any armed person, for the most part, cannot shoot as well today as in generations past because of the disapperance of the firearm as a staple in American life. For the last twenty years or so, kids have been at the helm of a video game control box instead of shooting birds, squirrels, rabbits, etc.... This has had a horrible impact on the shooting abilities of those who are introduced to firearms in their adult lives. I started shooting at about age 8. Two days ago I went to qualify with my trusty old S&W model 10. I shot a 290 out of 300. A year ago I shot a 285 out of 300 with the Beretta M9 at my Guard unit. Many men and women (civilian and Guard) cannot meet the minimum passing score of 180. In the military, they are offered many attempts. After many unsuccessful attempts, their records are forged to show a passing score (same with Physical Fitness tests, by the way). I've seen it many times. In my security job, those folks who cannot qualify are now starting to be fired. In the very recent past, their records were forged, too. So, as DSK wrote, the common thinking is to "pray and spray." I do not agree with this.

It is not too different from what happened at the FBI around 1990 or so. They wisely chose the 10mm as their primary duty cartridge. The S&W 1006 was going to be their duty weapon. Too many men, and especially women, could not handle the full power of the 10mm. They downloaded it. Somebody at Smith got the brilliant idea of shortening the case to accomodate the lighter charge. Voila! The .40 S&W. Shortening the case and reducing the energy also meant the size of the gun could be recuded from a .45-sized frame to a 9mm-sized frame. Have you noticed the FBI HRT and many Armed Forces special ops are slowly returning to the .45?

As for penetration, the 7.62 is superior to the 5.56. Somebody here was comparing 5.56 armor piercing to 7.62 ball. Pulllleeeeeeasse. Let's compare apples to apples.

Ballistic coefficient has little to do with penetration. BC measures aerodynamic efficiency. That's about it. If two bullets of different weights leave two barrels, with the same muzzle velocity, at the same time, both with the same BC, it does not mean they will impact their targets at the same time. This is where the weight comes in. A heavier bullet will impact first because of momentum. A heavier bullet retains more energy. It does not become evident until you get out to 600 or 700 yds and beyond. This is where light bullets "crap out" and heavy bullets keep on hummin' along.

In my opinion only, the 5.56 has been adopted to accomodate a new generation of video-gaming, mall-skateboarding soldiers who are inexperienced with arms. Give them a lot of bullets and a gun that recoils lightly, and hope like hell they hit something, of course not getting some hot brass tossed back and caught in their nose rings.

Rob



[This message has been edited by In service to His Majesty (edited 10-27-2001).]

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).]

"LAK
As to ball to ball I am comparing the current 5.56 and 7.62. Which version of Nato ball were you thinking of? spock"

Spock,

If I were going to make a valid comparison it would be FMJ/lead core bullets - and a separate comparison between rounds employing steel-cored AP bullets.

Ballistic coefficients do of course influence velocity loss. But there are 7.62 military loadings with longer/heavier bullets - I believe up to about 175 grains in AP, API etc with tungsten carbide cores which would compare to the heavier 5.56 loads with steel penetrators. The 147 or 150 grain 7.62 loads are really in the comparison class of the 55 grain FMJ 5.56.

No matter which way you cut it, the 7.62 is a superior cartridge. It is (as has been mentioned) a simple matter of physics.

Just for a relative comparison, take Federal's "American Eagle" .223 55 grain FMJ and their .308 150 grain FMJ load:

Velocity at muzzle, 100, 200, 300, 400 and 500 yds are as follows (from Federal Cartridge website - both test barrels 24")....

3240; 2950, 2670, 2410, 2170, and 1940 fps.

A FMJ .22 cal bullet travelling at 2670 fps is already moving down into the .22 Hornet area. Not to say it still won't kill placed in the right place, but hardly "devastating".

The corresponding figures for the American Eagle .308 150 grain FMJ run as follows...

2820; 2620, 2430, 2250, 2070, 1900 fps

Even at just 100 yards there is only a 300 fps difference. This between a bullet weighing 55 grains and a bullet weighing 150 grains. And that difference narrows to about 200 fps at 200 yards, and not much over 100 fps at 300 yds.

Of course there are heavier 5.56x45 loadings with bullets having better ballistic coefficients; but there are likewise longer heavier loadings in the 7.62x51.

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