FMJ yaw and upset performance

[Tony Williams]

Tony:

This one shouldn't be too hard to figure out. How much better does the 6.5mm bullet have to be before it shows a quantum improvement in exterior and terminal performance?

Start out with defining what that quantum improvement is and the rest will be easy to solve -- on paper.

What must the BC and velocity be to match in exterior terms and then multiply by about 50% before anything can be proven in real terms. When that is solved, then look at powder technology and finally bullet construction.

LR55

My approach is a bit different: I would start with the bullet, because its characteristics are the key to the success of any new round. There are two main aspects to this success:

1. Terminal effectiveness, in terms of straight-line penetration through various intermediate barriers (including car windscreens, a real headache for 5.56mm) plus rapid and reliable yaw and bullet upset on impact (I'd like to see the bullet begin to yaw within a couple of inches of penetrating a body, and completely turn over in order to travel backwards within 12 inches).

2. Exterior ballistics, in terms of a rate of velocity loss significantly less than 7.62mm M80 (probably around 0.50 BC).

With the bullet design settled it would then be easy to work back from the requirement to match the retained energy of the 7.62mm M80 at 1,000m, in order to decide what the muzzle velocity needs to be. The next stage would be to calculate the propellant load to achieve this MV in a specified barrel length, and therefore the case capacity, and finally the form of the cartridge.

This approach could be applied to any calibre, of course, but I think that the 6.5-7mm range looks the most promising. A 7mm round would probably show more reliable terminal effectiveness than 6.5mm at the cost of more ammo weight and recoil, and a steeper trajectory; you pays your money and takes your choice...

[stanc]

2. Exterior ballistics, in terms of a rate of velocity loss significantly less than 7.62mm M80 (probably around 0.50 BC).

With the bullet design settled it would then be easy to work back from the requirement to match the retained energy of the 7.62mm M80 at 1,000m...

We did some similar calculations on the old 65grendel forum. With the superior BC of a 123gr 6.5 Grendel load, it's easy to exceed 7.62 M80 energy @ 1000 meters. The trouble is that at the closer distances (<500 meters) where most infantry combat occurs, 6.5 Grendel doesn't come close to matching 7.62 M80 retained energy.

[Tony Williams]

We did some similar calculations on the old 65grendel forum. With the superior BC of a 123gr 6.5 Grendel load, it's easy to exceed 7.62 M80 energy @ 1000 meters. The trouble is that at the closer distances (<500 meters) where most infantry combat occurs, 6.5 Grendel doesn't come close to matching 7.62 M80 retained energy.

No argument with that Stan, but it really doesn't have to - at closer ranges it merely has to show a substantial improvement over the close-range calibre (the 5.56mm) in barrier penetration and terminal effectiveness, which should be no problem!

[RangerRick]

No argument with that Stan, but it really doesn't have to - at closer ranges it merely has to show a substantial improvement over the close-range calibre (the 5.56mm) in barrier penetration and terminal effectiveness, which should be no problem!

One thing that hasn't been discussed here in detail is barrel length. Is it possible to have one cartridge that will perform well in a 16 inch bbl for riflemen, in a 22-24 in. bbl on a squad machine gun like the M249, and of 28 in. (or more) in a heavy bbl version of the SAW for a platoon machine gun?

Designated marksmen could carry a rifle with 20-24 inch bbl with a PRS type butt and good optics.

What is the point of diminising return on bbl length in the 6.5 Grendel?

In a pinch, riflemen could break down linked belts to load mags or machine gunners could use magazines in the mag wells of the SAW.

[Tony Williams]

Barrel length is an interesting and somewhat controversial issue.

Clearly, if you adopt a general-purpose cartridge with excellent long-range potential, it makes sense if the gun you use it in is capable of exploiting that potential. Which is to say, has a barrel long enough to develop the velocity the round is capable of. On the other hand, the current trend with rifles is to use ever-shorter barrels in order to keep the guns compact for urban warfare and clambering in and out of cramped vehicles.

So there would seem to be three options:

1. Select an intermediate length barrel (say 16 inches) which isn't quite short enough to be really handy and isn't quite long enough for good long-range performance.

2. Choose a modular gun with a quick-change barrel and issue both short and long barrels - and hope that your troops don't get caught with the wrong barrel fitted if the tactical circumstances change suddenly.

3. Choose a bullpup, and for the same length gun enjoy a barrel eight inches longer than with a traditional design. This is by far the most logical choice, but the US seems to have something against bullpups...

[noone]

With the "big bolt" that is now available, pressures for the Grendel round could safely be increased. But, along with increased pressure would come increased cost for licensing of the big bolt's production. However, if a military was interested in this concept, I'm sure they could pay for licensing it.

That still leaves the issue of designing a bullet. There was one Nato country that deliberately used a very brittle 7.62x51 bullet and jacket design that was made to tumble shortly after entry, and break in half at the cannelure. Then there were at least two bullet fragments making at least two wound channels. This could also be done with a 6.5mm bullet.

As long as the money was available for research, I don't see any reason why a bullet couldn't be made with two cannelure type indentations so it would break into three pieces each weighing around 40 grains.

[JASmith]

No argument with that Stan, but it really doesn't have to - at closer ranges it merely has to show a substantial improvement over the close-range calibre (the 5.56mm) in barrier penetration and terminal effectiveness, which should be no problem!

I think Tony's point is on the mark. The challenge is to define the metrics so that we can go a tiny step beyond qualitative (read intuitive) comparisons and work toward quantitative assessments. We also need to remember that bullet design makes a huge difference. The good news here is that what is doable in 5.56 is also transferable to 6, 6.5, 7, and 7.62. The converse is largely true up to limits of scaling. For example, we won't necessarily be able to have the same ratio of meplat to bullet diameter in the 5.56 as we do for the 7.62 and maintain large-scale manufacturability.

This logic suggests that we ignore results that depend on a specific bullet design and focus on design potential as the caliber-based metric. For example, kinetic energy density is a good metric for comparing the potential for bullets of the same design to perforate thin barriers. Similarly, the momentum density is a good metric for penetration depth potential.

Lethality potential is a slightly more controversial subject. Fackler's and others studies show that the shape and size of the wound is an important indicator of average lethality. A lot of folks like to use kinetic energy to assess lethality. The problem is that KE does not give even a hint of the shape of the wound channel. For that reason, I lean toward a metric that captures both the penetration potential and the amount of material to cut a permanent wound channel. The metric is the product of the bullet mass and the momentum density. Go to http://shootersnotes.com/battle-rifl...minal-effects/ for more detail and a reference to Fackler's work.

My own assessments suggest that matching or exceeding the penetration and perforation potential of the 147 grain 7.62 bullet is easy in the smaller calibers. The lethality metric is more challenging because the smaller calibers carry a significant bullet mass penalty.

I've tried a couple of different metrics that use direct comparisons to existing rounds, e. g., M855 at 25 meters, M80 at 1100 meters, etc. , but at specified longer ranges. For example, one can ask the new cartridge to have a 600 meter lethality potential at leas as great as that of the M855 at 25 meters. These tend to be a challenge and the outcome suggests that the choice of threshold metric will have a tremendous influence on the calibers, bullet weights, and muzzle velocities that survive the filter.

I'm open to suggestions, and am intrigued by LR1955's suggestion to go 50% greater than the current standard (e. g., the M855 at the same range as the new cartridge). This would stress the perforation and penetration potential but might bring the required lethality metric more in balance with the other two.

[Tony Williams]

There was one Nato country that deliberately used a very brittle 7.62x51 bullet and jacket design that was made to tumble shortly after entry, and break in half at the cannelure. Then there were at least two bullet fragments making at least two wound channels. This could also be done with a 6.5mm bullet.

As long as the money was available for research, I don't see any reason why a bullet couldn't be made with two cannelure type indentations so it would break into three pieces each weighing around 40 grains.

The German ball bullet fragmented violently, but I'm not clear whether this was deliberate or accidental.

The problem is that the "Geneva legal" requirement excludes fragmentation (the British 5.56mm L2A2 ball has a thicker jacket than the original L2A1, specifically to reduce the probability of fragmentation).

Which is why I'm so concerned that the bullet must yaw rapidly on impact. If it just punches a neat hole straight through, then the effectiveness will be limited unless it hits something vital. If it yaws rapidly and travels sideways through much of the body it will tear a much bigger wound channel, giving a greater chance of hitting something vital or of rupturing enough blood vessels to cause more rapid bleed-out. A long, low-drag bullet will tear a bigger wound than a short one when it's sideways, which in an intermediate calibre would compensate to some extent for the reduction in calibre and mass (the 123 grain 6.5mm Lapua is longer than the 7.62mm M80).

[stanc]

The German ball bullet fragmented violently, but I'm not clear whether this was deliberate or accidental.

I'm inclined to think it may not have been deliberate, but rather incidental to using mild steel as jacket material. US M80 Ball has been produced in two flavors, one with a relative thick jacket of gilding metal (which yaws, but does not fragment), and the other made of thinner, mild steel (which yaws and does fragment!). I've seen belts of Vietnam-era M80 that had GM jackets, and other belts with steel jackets (it varied according to manufacturer). All of the recent M80 I've seen has had steel jackets.

[stanc]

FWIW, attached is the wound profile of the .303 MkVII.

[Tony Williams]

Thanks Stan, the .303 seems to compare pretty well with other FMJ bullets, although an even earlier onset of yaw would obviously be preferable.

[LRRPF52]

Myths about 5.56 Ineffectiveness/Need For New LMG

Tony,

I might suggest that most of what is read about 5.56 not being effective, even at close ranges, is totally opposite of what I've personally seen with the cartridge in real world wound ballistics on enemy combatants and "friendly" fire incidents. As a rule, every 5.56 injury/death I have been able to analyze has been characterized by unusual tissue destruction, and generally avulsive (ripped/torn/pulled flesh) effects to soft tissue and extreme bone fragmentation. I have seen countless magazine articles pre-texting an argument for a new caliber with statement about how "Everyone knows the deficiencies of 5.56 on human targets", etc., which is why the credibility of most gun rags has dropped to "not worth picking up" for me anymore-even though I grew up on a healthy reading diet of them.

I've seen 5.56 M855 canoe a man's head, shatter arms, legs, pelvis's, and feet, sometimes after going through thin walls and bouncing off SAAPI plates. Most of those have been fratricidal, unfortunately. Is it my number one choice for making 400-500m shots? No, it isn't-but it is for most of what a rifleman would encounter in the engagement distances that riflemen are tasked to operate in, while next to their SAW, MG, and DM counterparts. I don't like thinking of shooting much else in the house or courtyards-especially as the caliber increases.

I really like the 6.5 Grendel as a cartridge that pretty much duplicates 7.62 NATO ballistics, but with much less weight, recoil, and a smaller receiver/magazine system. I do not think of the 7.62 NATO as a 1000m-capable cartridge, though it is often listed as such. I think 600m is a more realistic distance for 7.62 NATO and the Grendel, having shot both of them enough to reach that conclusion in realistic wind conditions. I have made much farther hits with match .308 loads out of trick rifles, but the winds were dead or canceled at chance opportunities in my favor for those hits, and they were rarely 1st-round.

I recently wanted to test the lighter weight 123gr Scenars in my .260 Rem out to 700 yards (640m), running them at higher velocities. Even at 2960 fps, I was disappointed in the 123 Scenar at that range out of my custom 22" GAP AR10. I had much better results with the 130gr Berger VLD's going 2850 fps, but the same ballistics program showed the 123's doing better for wind deflection at that distance. I was skeptical, but needed to see the actual results for myself. With the shifting wind speeds, even by maybe 5 mph at half value, I was still one-minute of wind off target either way at 700 yds with the 123gr Scenar. A Grendel will never get a 123 near that speed, so I would list the 600m range as a limit for 1st round hit probability with the Grendel for a highly-trained shooter/spotter team with 10 mph winds. A standard rifleman would just be spitting in the wind...

It would be nice to have a Lightweight Belt-fed Machinegun in Grendel to replace the M240 GPMG for dismounted soldiers, if a lower-cost bullet could be made for it with a long tracer endurance like the 7.62 tracer. That would allow SAW gunners and 240 gunners to carry the same MG, creating a new class of machine-gunner, who is capable of supporting the Squads and Platoon without losing current capabilities. Maybe a larger case-capacity would be best for the MG, but then barrel life would most likely suffer. I've made this argument before about more of a need for a lightweight Universal Machinegun, not a replacement for the M4 carbine. We need LMG's that allow Joe to shoot and move with his buddies carrying lightweight carbines, not a new carbine.

LRRPF52

[Tony Williams]

Thanks for taking the time to post that. I don't have any personal experience of examining 5.56mm wounds, and I don't doubt what you say. I've also been careful (I hope) to say that, according to the large number of reports I've read from both combat and lab testing, the problem is not that the 5.56mm is ineffective (because it can be extremely effective) but that it is not reliably effective. Of course, no bullet will put down a man first time every time, but the 5.56mm seems to fail more often than most, for reasons which have been demonstrated in gel tests - that unless it is already yawing before impact, it will punch a small hole straight through. The figure I have seen from test results is that 85% of the time, the M855 bullet does not even start to yaw after impact (if it yaws at all) until it has penetrated at least 4.7 inches of gel.

That's on top of the other issues, to do with the 5.56mm's poor barrier penetration, lack of suppressive effect and lack of effective range (which different military sources put at anywhere between 200 and 400 metres, depending partly on barrel length).

These issues with the 5.56mm form only one of three reasons to consider a long-range intermediate round to replace both 5.56mm and 7.62mm.

The second reason is, as you mention, to replace 7.62mm guns and ammo with something with a comparable long range performance but with significantly less weight and recoil. This motivation has been moving up the agenda in recent years, given the nature of the fighting in Afghanistan, and is now arguably stronger than the case for replacing 5.56mm.

The final reason is the advantages in replacing two calibres and weapon families with one. This would halve the number of different firearms which an infantryman has to become familiar with, saving money on procurement, training and support. It also ensures that all infantrymen are equipped with a rifle or LMG which can be effective at any range, should the tactical circumstances change suddenly, and everyone in a section will be carrying the same ammo (which some soldiers I have heard from regard as an important advantage).

Whether anything will come of all this I don't know, but the calibre debate within the US military and small arms community seems to be hotting up, in the light of the recent ARDEC report and the reported decision over LSAT. I am observing with interest!

[JASmith]

Tony,

Before you go too far into mea culpa, many of the events recounted by LLRPF52 involved the bullet hitting something immediately prior to entering the body. This means that the bullet is highly likely to be significantly yawed and possibly even upset by the prior impact.

The conclusion one can draw is the almost universally accepted one -- "The 5.56 does well within the first 100 or so meters."

The question we should address might be "How far out do we want the the new cartridge to have the potential for the effects described by LRRPF52?"

I would also concede that this question might be mooted by the desire to have the lethality at least equivalent to that of the 7.62 M80 round at 1100 meters.

[LRRPF52]

Gents,

I must clarify that there was only one event that involved 5.56 penetrating a thin barrier. The rest were all from muzzle to target. Basically, with the single barrier incident, a SAW gunner was left outside a light-framed building when he should have followed his team, which was the trail team in an Airborne Infantry Squad of 9 men. The lead team had already penetrated the building and pushed into a 2nd room. The SAW gunner from the lead team fired a burst into a plastic E-type target, and the rounds went through the wall, which was made of thin plywood that was dried out from the extreme heat. His forearm and leg were severely injured with significant tissue destruction, bone fragmentation, and blood loss. He survived, but looked like Frankenstein in the areas that needed reconstructive bone and various other surgeries.

That was from a Commando barrel SAW pushing M855. His radius and ulna in the left arm looked like someone had completely fragmented each bone, with only the styloid processes, radial head, and olecranon process of the ulna being recognizable on his x-rays. Our medics and PA used ace wraps to form compressive pressure dressings, and evac'd him successfully. He ended up with pins forming his radius and ulna in that arm, and I think the soft tissue damage to his leg just left heavy scarring and some muscle tissue loss. The PA said it looked like at least one round had skipped the SAAPI plate on his IBA. That could explain the yawing, as I doubt that there was much yawing after going through such a thin piece of wood. There were some direct connects without the SAAPI plate involved though.

I have also seen M855 cut through very thick and wet trees in Panama like they weren't even there, which really surprised me, so I'm skeptical of many of the claims about weak barrier penetration with that round on trees, although I know it is quite limited on cinder block and solid brick. All I know is that after seeing that, most trees went from being "cover" to only "concealment" in my mind. I would not count on a tree to protect me from 5.56 or any other high power rifle caliber.

The guy that got his head canoed was in the Korean Peninsula, and he was a bona fide bad guy. A ROK Army soldier shot him with a Daewoo K2 with the South Korean made M855, which is manufactured to the same specs. That incident really woke me up to the reality of what 5.56 can do, and nothing anybody says about it will change that. As far as reliable performance goes, every person I have seen that took a 5.56 round had a very bad day. I have rarely seen or heard any of my friends complain about a clean 5.56 injury and the resulting ineffectiveness, though I readily admit my experience is limited to less than a dozen incidents where I was able to witness the details of those injuries/deaths on actual human targets.

Gel tests will rarely correlate to humans, since there is such a wide quality in tissue density and dimension on human torsos, arms, and legs. Gel tests rarely involve bone simulation, or body heat, and they don't compartmentalize the various layers of fascia, sinew, connective tissues, vessels, skin, etc.

What this means from a practical standpoint in my mind is that I lean towards the school of thought where I divide the human target into thirds, and aim for the smallest point within the center third of center of mass, regardless of how the target is presented, and put as many well-placed rounds into that point until the target goes down, regardless of what caliber is being used. That is what I taught soldiers I was responsible for, and many of them have used that concept with lethal results.

If we want catastrophic hydrostatic effects on human tissue at even 400m, you are pretty much talking about .338 LM with some type of projectile that would at least toe the line of the Hague, unless you use API. For an assault rifle, I think 100m is the threshold of expecting that type of performance since you need at least 2700fps to make that happen with FMJ's. That doesn't bother me at all, as long as Joe can put a hole that bleeds well in his target past 100, and carry plenty of it with minimal space/weight.

For AOR's commonly found in Afghanistan, it might be appropriate for small unit leaders who deal with dismounted patrolling to spill in a heavier mix of 7.62 rifles/carbines, but not too heavy. You could also equip DM's with SPR's and the Mk262, but the real area of weakness as far as weapons goes is the weight and portability of the M240. It would really be great to have a smaller pig that duplicates 7.62 ballistics, with less recoil and lighter ammo. That is what would make Joe happy, because it would increase the maneuver capability of gunners and the unit overall, so effective suppressive fire could be brought into play against the well-coordinated far ambushes that are the forte of the Muj/Taliban.

LRRPF52