Terminal effect differences?

Bigger and faster is always better. The 7.62 NATO has more displacement and energy than the 5.56. The 7.62 x 39 has much less energy than the 7.62 NATO. Especially at longer range.

I am by no means an expert on this subject and will just say what I have heard around and let others correct me as needed. The 7.62x51 NATO (.308) will hit VERY hard out to what many consider it's max effective range of 800-900 yds. Up close and personal, it will hit and go through and through without a problem. The 7.62x39 will hit harder than the 5.56x45 NATO up close, but loses the long range battle. Now what I have heard but have no personal experience in, is that the 5.56x45 NATO will hit and tumble when it hits its mark.

Any of these rounds have the ability to knock down their target with one shot when used within their effective ranges and when a well made shot is taken.

Blackhawk down....is a movie so you can't believe everything you see. (although it has been so long since I have seen it there maybe some legitimacy to it)

I have never served in the military so I don't know if the statement I am about to make will hold true, however, here goes nothing.

If I was put in a kill or be killed situation (i.e. combat) I would shoot until the threat was neutralized. Even if one shot with the 5.56 M16/M4 was fatal, adrenaline might have already pulled the trigger another two times.

When I started out doing military duty in the mid 70s, we had the A1 M-16s using the 55 grain bullet and the 20 inch barrel with a 1 in 12 twist rate. Plus some M-14s and M-21s. We also had a few shorty M-16s which were referred to as CAR-10s or CAR-15s in those days. They were know as being handy, but mostly for creating a huge fireball sized muzzle flash.
We also had M-60 machine guns (the pig)
During the Grenada Invasion (Oct 83) we (my unit) still had M16A1s, the Marines I personally saw had A1, although they were supposed to be getting the new A2s.
I did not note any huge difference in wounds between the 7.62mm NATO M-60 hits and our M16A1 hits.

During the 1989 Panama invasion, a bunch of us reservist types had M16A1s while all the full timers had the A2s. I did note a difference in wounds from the old A1s and the new A2s. The A2s seeming to be more like stabbing somebody with a knitting needle. I figured this was because the long 62 grain green tip bullet was being over stabilized by the A2s 1 in 7 twist rate.
The M-60s MG wounds that I saw seemed to be significant in comparison, but we attributed that to being in a city environment and most of the bullets had bounced off the pavement or building sides before striking the enemy. So they were either deformed or tumbling.
During later tours in the 90s and 2000s the short barreled M4s with over-stabilizing 1 in 7 twist replaced the longer and higher velocity A2.
At that point the wounds generated by the 7.62mm sniper rifles and the M-240 Mgs seemed to be noticeably more severe.

There are various test photos out there done by labs who want to sell stuff to the military and by the military so they can justify spend more money on new stuff....

Most involve shooting gelatin blocks. Although I have never been attacked nor do I know of anyone being attacked by gelatin blocks.

Although it is all relative.
In the 1890s the Brits compared their fragmenting Dum-Dum arsenal bullet wounds to the old wounds produced by the Martini-Henry type single shot rifles in 45 caliber that they had previously been using. They discovered that the 303 British with soft point ammo did not make a wound any worse than the huge and slow 45 caliber single shot rifles had made. This test was carried out because the Germans, complained that the Brits Dum-Dum type ammo was inhumane.
Thus leading to the 1899 Hauge treaty which banned Hollow and soft points for general warfare.

Looking at the illustrations found on this page http://www.firearmstactical.com/wound.htm (Obviously I can't post the illustrations or even the links to them) you can find ballistic testing results on the cartridges you are interested in.
It's pretty obvious that the two 7.62 cartridges give much deeper penetration than the 5.56's. The permanent cavities also come at a deeper penetration depth. No real surprises there, I suppose But the military 5.56's appeared to fragment at a rate of about 50 percent in these tests. Both 7.62's appeared to exhibit some tumbling and this apparently contributed to the permanent cavities in both cases.
Interesting tests!

Actually, the weapon that was most noted for not working well in BHD (the book) was the 7.62 NATO, used in the M60. The M14 v. M16 was the remark of one of the Delta guys.

I would imagine the hemmorage would be worse with 7.62 Nato even with FMJ ammo. Much larger projectile flying at the same speed would be worse. Only my excperience is from hunting wounds and trauma.

ramsfan said:

What is gained in the terminal effects (using FMJ ammo only) of a .308 over a 7.62x39 or 5.56?

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Even with FMJ ammo, a lot depends on the bullet design. For example, 7.62x51 (.308) M80 ball against a lightly clothed opponent isn't all that impressive compared to 5.56x45 M193. But if we use say, Wolf .223 FMJ and West German 7.62x51 FMJ, you'll see very different results.

There are a lot of variables in wounding. And while the permanent cavity is important, the temporary cavity can contribute to wounding as well - especially with inelastic or fluid filled organs.

Float Pilot said:

The A2s seeming to be more like stabbing somebody with a knitting needle. I figured this was because the long 62 grain green tip bullet was being over stabilized by the A2s 1 in 7 twist rate.

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It is impossible to spin a bullet fast enough to make it stable in the human body. The science behind this is explained in these links:
http://ammo.ar15.com/ammo/project/term_tighttwist.html
http://ammo.ar15.com/ammo/project/term_twistduh.html

There are a couple of reasons why you might see different performance between M193 and M855, such as more complex bullet construction for the M855, not enough depth of tissue and fleet yaw; but 1:7 is nowhere near fast enough to prevent a bullet from yawing.

Most involve shooting gelatin blocks. Although I have never been attacked nor do I know of anyone being attacked by gelatin blocks.

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Ballistics gelatin is used for testing because it is uniform. If you shoot a person, a lot of small variablse can affect terminal performance - say a bullet strikes a rib and deflects a small amount - depending on the deflection it might go through the heart or away from it - meaning the same shot with the same caliber in the same location might have two dramatically different results.

While ballistics gelatin can't show you precisely what any given shot will do to a human body, it can establish some measurable performance standards that are useful in determining what works on people. For example, the FBI has figured out that if a bullet penetrates 12-18" in ballistics gel and makes a big hole, it usually does a good job on 150-250lb mammals, given adequate shot placement.

And at the end of the day, shot placement is still the #1 criteria that determines how effective a bullet is.

In this case, would the more severe wounds created by the 7.62 be due simply to the larger diameter bullet (which doesn't seem like that big of a difference), or does the additional energy of the 7.62 start to contribute in some way?

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If you take two bullets that don't yaw, one being 5.56x45 and one being 7.62x51, the 7.62x51 will have a bigger temporary or stretch cavity. It will stretch tissue more and can burst fluid filled organs - if tissue is stretched past its elastic limits, it will tear and become permanent damage. If not, it gets bruised maybe; but returns to its previous position once the bullet passes.

This is one of the reasons fragmentation is so effective with rifle bullets. Think of a rubber band - stretch it and not much happens unless you stretch it past its breaking point. It snaps right back into place. Now stretch a rubber band to just shy of its breaking point and start poking tiny holes in it with a needle. What might have normally been only a temporary cavity instead becomes a permanent cavity as the stretched tissue detaches.

Yes, kinetic energy is transferred whether the bullet yaws or not, just the amount transferred will change. As far as tearing elastic tissue, it of course depends on how close the tissue is to the bullets path. I would expect that an organ, (e.g. a lung) would collapse more easily than a muscle would tear due to a stretch cavity, but don't quote me on that because I could very easily be wrong.

The OPs example was a military ammo situation but heres Hornady's civilian TAP ammo gel tests.

http://www.walsworthdigipub.com/hornady/hornadyle.html

The 7.62x39 tests are a couple of pages past the .308. The .308 with the 155 A-MAX is a monster bad guy dropper. See how the 5.56 beats the 7.62x39 even with Hornady's 123gr V-Max bullet?

From Float Pilots observations, it sounds like the 62gr green tips and the rounds fired from the A2s and M4s would exit before they tumbled.

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Those of us who had an interest, and in some cases a duty, to note and observe thought that the M4s 14.5 inch barrel, along with the M-855s lower velocity & nice stabilized BC, led to the observed wounds being less than spectacular. Particularly when the enemy was engaged at longer ranges. (200 plus meters)

Unfortunately multiple reports either go unheeded or result in more muti-million dollar BS projects from defense contractors. In the long run, the stay home jello shooters win out. Plus the currently political Czars have no interest in the subject.

The bruising might be bad, but any doctor's first priority will be to stop the bleeding and then worry about missing/torn tissues. The bruising would probably fall later on the priority list

There's a lot more to a main battle rifle cartridge than perfect conditions gel performance or perfect condition flesh performance. You should always have a bit bigger bullet than what's minimum neded to kill a man.
You don't always have perfect conditions, the enemy is not always runing around naked right in front of you. Intermediate barriers, doors, cars, thick brush, weeds, cold weather, heavy clothing, short barrel, etc. This are all things that can dramatically reduce the ability of your bullets to kill the enemy.
The AK round is the living proof that bigger bullet works better.
It plows it's way to the target. Even with that ancient bullet design and at that sedated speed, it still gets the job done.

Ok for the one shot drop: BOTH will kill with one shot placed well. The 7.62 has more margin for error because it will release more energy into the target with military ball rounds which translates into more trauma.

If 7.62x51 FMJ encounters soft tissues only and exits the body before it yaws it will produce a wound not much more severe than .32 ACP FMJ - it will crush only those soft tissues it comes into direct contact with.

So even without the bullet yawing, it could still create enough of a stretch cavity to have some effect?

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No - the bullet has slipstreamed contours which allow it to travel through soft tissues without substantially disturbing them. Fackler's wound profile illustration shows a maximum temporary cavity of about 1" in diameter before the bullet yaws - that translates into a little less than 1/2" of soft tissue stretch.

From Float Pilots observations, it sounds like the 62gr green tips and the rounds fired from the A2s and M4s would exit before they tumbled.

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Many bullets may have merely broke in two at the cannelure and only the largest piece exited the body. Then all that would be visible externally is a small entrance wound and a small exit wound - which might lead one to incorrectly conclude that the bullet "drilled right through".

The same would be true for a bullet that fragmented substantially with only a small fragment exiting.

It also sounds like anything I might have read or heard (no specific source) about muscle turned to jelly or lungs liquified by a fmj bullet from a military rifle was more fiction than fact.

It does not sound like a stretch cavity would be so destructive to elastic structures.

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The temporary cavity produced by a yawing 7.62x51mm FMJ bullet can be as much as 8" in diameter. It has the potential to stretch elastic tissues beyond the limits of their elasticity and to the point where some appear to have been "turned into jelly" by what is in essence blunt trauma.

The explosive-like effect of temporary cavitation produced by a varmint bullet in a small animal's body often exceeds the size of the animal and the animal is literally torn apart by the violent effects of temporary cavitation.

Just trying to understand exactly what makes the terminal effect 7.62 or .308 (drops them with one shot) better than the 5.56, or if that is really even true.

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Greater mass and substantially surface area when the bullet yaws.

Shawn, you're points seem sound and I've certainly not researched the issue much.

However, one thing I've noticed while shooting liquids such as 2-liter or 20oz bottles of water is that the impact seems quite a bit more dramatic between a .32acp and 7.62x51.
The liquid-filled container appears to fall over and leak when shot with my P32 (S&B 73gr FMJ) while the same container explodes into oblivion with a 147gr FMJ from my FAL.

I'm guessing the 4-5" of water the slug is traveling through isn't reacting to any yawing. It's hard for me to imagine this difference in effect wouldn't transfer somehow when the target is a human.

IMO an 8" cavity is huge, I'm not a doctor but I would venture an educated guess and say yes, that would cause permanent damage. It seems like that would be just too large of a cavity, and push those vital organs around (into each other and the rib cage) too much for there to not be permanent damage. I know that I don't have 8" of spare room in my rib cage for organs to move around in.

In my experience both rounds, 7.62 nato and 5.56, produce similar wounds and most of the time in country you couldnt tell who was shot with what by looking at the wounds.

Standard M855, aka green tip, has been known to have huge differences in terminal effects between lots and different rifles. Depending on how it hits the bad guy it either yaws quickly and is very effective or it can yaw late which might be outside of the bad guy. Thats why there is a big push for the new rounds in the Army and Marine Corp.

I have stated several times here that the only person I have seen shot through the chest with a rifle and live, was shot with a 7.62 Nato round out of an Abrams coax. It was a fleeing RPG gunner that was part of an ambush that hit us one night. He was hit in the upper right back, around the bottom tip of his right shoulder blade. The bullet then exited his left nipple. He was found about 30 minutes after the ambush still alive and Im pretty sure he lived.

That doesnt mean that 7.62 Nato is weak, it just illustrates that people can actually be very resilient when critically wounded.

I have seen several people shot through the chest with bothe 7.62 Nato and 5.56 and take a little while to expire, but none of them were a threat after being shot.

5.56 is very destructive when it yaws and fragments. The new Mk318 and M855A1 are supposed to reliably fragment unlike current ammo. Looking at the design of the M855A1 I can believe it.

Both M855 and M80 need to be updated to more effective rounds.