[Supertroll]

I have a question on these two rounds.

I was told by an MP at a range that they've tested an M-60(7.62) and an M-16(5.56) on a steel plate, I'm not sure of what distance - but I was told the 7.62 round bounced off, and the 5.56 round punched right through. Now people are arguing with me, and I'm wanting to make sure if I'm in the wrong or not.

Scientific explanations appreciated.

 

[Jeffvn]

Assuming certain factors, I believe it is possible.

Certain .224 bullets have a higher sectional density (and corresponding penetration power) than .308 bullets (like the 77 and 80 Sierra Grain MK - as compared with a 150 grain .308 Sierra MK of Gameking). Under these circumstances the .224 will penetrate further than the .308 at identical velocities. If the .224 is flying faster the the .308 (and it usually is by a considerable margin) it may well penetrate the plate and the .308 will not (the further you get from teh target, the more energy bleeds from teh .224 as compared with the .308, so I think the range had to be fairly close, less than 300 yards or so).

Although I believe the bullet's frontal area is/may be part of the Sectional Density formula, I think it is worth noting that the frontal area of the 7.62 is 140% larger) than that of the .224, and you see that the energy developed is focused and transmitted into a much small area.

Its now time for the experts to smack me around and call me names. :wink:

 

[Nekekami]

It can happen under certain conditions, but generally speaking, the 7.62x51 will have somewhat better penetration.

For example, taking your example, with a 5.18g(80 grains) 5.56 bullet with a muzzle velocity of 930m/s, you get a total energy at the muzzle of 1816j. The total area of the bullet, seen from the front, is 24.2mm². Thus you get around 75.04j/mm².

For the 7.62 bullet at 9.72g(150 grains), at a muzzle velocity of 850m/s(Fairly common for military ammo), you get a total energy at the muzzle of 3511j. The total area of the bullet, seen from the front, is 45.5mm². Thus you get around 76.995j/mm²

 

[Jeff_850]

i have herd that the 62gr fmj penetrator round in the 5.56mm could penetrate body armor more reliably at 600m while the standard 7.62mm 147 gr fmj (m80 ball i think)
the 7.62mm is a much more powerful round, but is much thicker but usually will have better penetration, however it was comparing standard rounds to armor peircing rounds
if they compared whatever 7.62mm that is used to be armor peircing, it would probably do a lot better than the 5.56mm

 

[Supertroll]

Well.. there has been claims that one fired an M-16, the round went through. I'm not sure how thick the steel plate was... and they fired an M-60 at it, and the bullets didn't penetrate.

 

[Nekekami]

Jeff_850:

Out at 600m, it would have to be a very light vest for the 5.56 to penetrate, since the energy has decreased very much out at that range.

Supertroll: I'm kinda skeptical to that happening.

 

[Jeff_850]

ya heh thats what i figured but thats all i herd from some article, dont remember where

 

[Jake S]

Actually it would sort of make sense for standard FMJ bullets (maybe not AP) as in the .224 bullet there would be considerably less surface area of the projectile in contact with the target, ergo less friction to slow down the bullet, allowing it to cut through more easily. This is one of the reasons that the 9mm will in almost every case outpenetrate the .45.

I read the same thing in an old Guns&Ammo magazine from the 1960's. They compared the then-new M16 and its issue ammo to a M14, shooting through ammo cans filled with water (the one hit with the .308 put a nice neat hole in both sides, the one hit with the .223 exploded!) and armored helmets- same story. The one shot with the M14 dented it, the one shot with the M16 went right through with no problems whatsoever.

Merely what I heard/think, I am in no way an expert.

 

[Nekekami]

Jake S:

No, it's not friction that matters. What matters is the amount of energy for a given surface area and momentum.

And as for the Guns&Ammo magazine, it must have been a lot of hype. First of all, as I pointed out in my example, even a fairly standard 7.62x51 cartridge gives you more energy/mm² than a quite heavy 5.56x45. Second, water cannot be compressed, so the 7.62 bullet displaces more water than the 5.56 bullet with at least the same force, due to the larger volume of the bullet. So even if it makes two holes, the can should pretty much "explode" if either bullet hits it. And, as for the helmet. If the 7.62 could penetrate the water-filled ammo can, but the 5.56 couldn't, the conclusion is that the same thing goes for the helmet(And it sure as hell matches what I've seen in the ammo tests we've done).

 

[Jake S]

Well I didn't write the article or do the tests. Just relaying something i saw to those who had posed the question. And I can't imagine G&A would fabricate the story, considering their reputation in the American sporting magazine genre, and their review showed how powerful and efficient the cartridge was in comparison to the old .30 cal's, which was quite the opposite of what most people were saying about the gun at the time. I don't see a reason for them to make up the information and tests to counter the current common opinion.

 

[Nekekami]

The magazine itself might not be to blame, the article author(s) could very well be to blame.

 

[FLEA]

!

My only though on this was when we shot a steel handgun target with a m-14 and a m4. The m4 put a hole in it but the m14 dented it. Why....I figure its because it is one of those swing targets and the size and energy of the .223 just went right though while the size of the 7.62 just made it spin. Did the article say anything about how the target was anchored?

 

[Nekekami]

Flea:

Hmmm. Bullet shape could have something to do with it.

Whenever I'm instructing the FBU(Voluntary officer training. A course for 16 year olds and up who want to become NCO's or want to apply to officer training) in how to use the AK4 and AK5, we inevitably end up with comparing the power of the various cartridges, and the 7.62 more or less always has better penetration, except for some flukes.

Talking about flukes, the most interesting and eye-opening one was the time I hit an insert plate for a class 3 vest with our subcaliber round at a distance of 150m.... And it didn't penetrate...The 19 following shots all penetrated.

 

[DR308]

Hole ver's dent

Flea: What kind of rounds were fired out of the M-4? And what kind out of the .308? Chances are the .223 rounds were of the 63 grain ss-109 rounds that have a steel core. And mabey the .308 ammo was lead core. In which case, that would explain it. Boy's---- you got to love this forum!!

 

[FLEA]

!

If they were ss109's I would of understood...nope just regular FMG rounds.

Does anyone think the fact that the target was a spining handgun one have anything to do with it? I could only think that the size of the 308 couldn't punch through the target fast enough before it would spin like the 223 could.....The guy at the range took away his target after the first hole went through it so I could really test out any theories.....to this day it still bugs me.....I think Im gonna have to go buy one and do some testing :wink:

Well sometimes the laws of physics are just broke.

 

[Jake S]

I'd say it was bullet style, not the swinging target that allowed the .223 to go through. True story- Me and my uncle were up at the target range him (my uncle) and his neighbor have constructed up in a large former gravel pit. Another family friend was up there with us to shoot his new Winchester model 70 .30-06. We have steel targets set up at 25 yards for the .22 long rifles to be shot at. They are made of 3/4 inch thick tempered steel plates. In all of his brilliance, Mr. .30-06 suddenly whirled and hit with a 180 grain soft point .30-06 round the 25-yard swing target. After a long chewing out about the dangers of ricochets, we looked in disbelief at the target. Hole straight through it. 3/4 inches of solid steel, a lead soft point hunting bullet. A perfectly concentric .30 caliber hole through the center of it. Saw it with my own eyes. That target is sill up there, if you want to see it, I will drop everyhting to prove it to you. Weird. Of course Army specs say a .30-06 FMJ will go into 11 inches of oak at 600 yards. But still weird.

And the targets in the magazine, the helmet and the ammo can, were simply placed on the ground, not anchored in any way.

Jake

 

[boisedarc]

I'll take a wild stab at this. At a given distance with the 308 the heavier bullet striking say a steel plate, the energy is displaced in say a 15" diameter circle. With the 223 the lighter bullet striking a steel plate the energy is displaced in a much smaller circular area say 3". Thus you have more energy concentrated in a smaller area with the lighter bullet. But like I said at a certain given distance, to say that the 223 would out penetrate the 308 at any distance out to even just 300 meters would be a foolish thought. Let me know what you think about this theory

 

[FLEA]

!

boisedarc:

Yeah I was thing around the same lines you were.... thats why I asked.....and the target was about 80 yards out.

 

[Jeff_850]

boisedarc:
what you are saying makes sense and i agree with it, .308 has much more bullet momentum, id guess around 2.5-3 times more? too lazy to get out a calc
however the .308 is much wider and therefore does project all its force into a much larger area
the .223 is much more concentrated and at close range, hasnt lost most of its velocity from its lower ballistic coefficient

 

[DR308]

OK: I have a true story also. It happened back in 1987 when I was at gunsmithing school in Troy N.C. One of my classmates whose initials are JOE PALIN, took one of his rifles out to the school range to try it out. With him he also took a 1 inch thick steel chicken. The rifle he was testing out was a .458 KT Magnum!! He put the chicken out at 25 yards, went back and picked up his rifle, aimed at the chicken, and pulled the trigger. He came back up from the range and stumbled up to me while I was working on the lathe. He asked me to check if his rifle blew up. It did not. But he was pretty bloody from his face to his belt. I took him to the hospital and they removed the better part of that .458 out of his face, lips, and belly. To say the least, he was VERY lucky he did not kill himself. I went down to the range to get what was left of the chicken. Man, what a sight! There was a huge cone shaped hole ALMOST all the way through it. Thats right, I said ALMOST! It did not penatrate through. Just about, but not quite. The outer rim of the hole had melted pellets of steel attached to the rim of the hole. It looked like the steel had erupted from the hole and the molten steel had cooled before it could fall to the ground. Looked pretty cool really. But here we are talking about a 305 grain FMJ bullet traveling at right around 3000 fps, and it DID NOT go through it!!! Sometimes there is just no telling how a bullet will act. Beats me. :shock: