FMJ yaw and upset performance

[Tony Williams]

I am interesting in promoting the idea of a long-range intermediate military cartridge capable of replacing both 5.56mm and 7.62mm NATO rounds.

In order to be "Geneva legal" without getting into lots of arguments with lawyers, the bullet needs to be of the FMJ, non-fragmenting type - definitely not with an open tip. The wounding mechanism will therefore mainly be via rapid and reliable yaw and upset on impact: the bullet should start to yaw within about two inches of entering a body, and should have entirely turned over and be travelling backwards by about 12 inches.

The problem is, I have read in a British report that in a gel test by Alexander Arms of an FMJ bullet fired from a Grendel case, it did not start to yaw until after penetrating several inches, which is not good enough.

So I really have a two-part question here:

1. Is it possible to design a low-drag 6.5mm FMJ bullet of around 120-125 grains which exhibits rapid and reliable yaw and upset on impact?

2. Is it possible to achieve the same performance using a lead-free bullet, since that seems to be a growing military requirement?

[Hoot]

The two easy ways to encourage upset upon impact with soft tissue is to either cast an air pocket at the front of the bullet when you swage it. The tip doesn't have to be open, just have air immediately behind it. The second is to choose a body style with a short ogive and a pronounced boat tail, think M80 ball.

Hoot

[LR1955]

The two easy ways to encourage upset upon impact with soft tissue is to either cast an air pocket at the front of the bullet when you swage it. The tip doesn't have to be open, just have air immediately behind it. The second is to choose a body style with a short ogive and a pronounced boat tail, think M80 ball. Hoot

Hoot:

Got it backwards. M-80 has a very long ogive for its overall length and a short boat tail. However, that combination does make it pretty unstable when it strikes something but it still must penetrate close to a foot of gel before it starts to tumble. The old 5.56 M-193 had the same basic shape. The problem with these shapes is that they are not real good in exterior performance due to their design either.

LR1955

[LR1955]

I am interesting in promoting the idea of a long-range intermediate military cartridge capable of replacing both 5.56mm and 7.62mm NATO rounds.

In order to be "Geneva legal" without getting into lots of arguments with lawyers, the bullet needs to be of the FMJ, non-fragmenting type - definitely not with an open tip. The wounding mechanism will therefore mainly be via rapid and reliable yaw and upset on impact: the bullet should start to yaw within about two inches of entering a body, and should have entirely turned over and be travelling backwards by about 12 inches.

The problem is, I have read in a British report that in a gel test by Alexander Arms of an FMJ bullet fired from a Grendel case, it did not start to yaw until after penetrating several inches, which is not good enough.

So I really have a two-part question here:

1. Is it possible to design a low-drag 6.5mm FMJ bullet of around 120-125 grains which exhibits rapid and reliable yaw and upset on impact?

2. Is it possible to achieve the same performance using a lead-free bullet, since that seems to be a growing military requirement?

Tony:

In answer to your questions. I am sure both are possible. I am also sure the same can be done with 5.56 and 7.62 at a much lower cost. And I am also sure that what ever design got developed that it would not increase battlefield lethality.

For the lead free designs, that too is possible. The same is possible with 5.56 and 7.62.

Same goes for designing something that starts to yaw in two inches. Am sure it can be done given enough money. The result would probably be dollar a shot ball ammo whose hit probability is less than a similar redesigned 5.56 and 7.62 because anything it hits on the way would result in it becoming grossly unstable.

Still haven't commented on some new VLD design ball round out shooting surface danger zones on ranges. Or the basic weakness of the Grendel bolt and the lack of reliable magazines.

LR1955

[Tony Williams]

The British analysis I was reading reckoned that a relatively long bullet with a sharp point rather than a flat meplat (but not so sharp as to be easily damaged) aided rapid upset. Obviously, a steel core helps to increase the length but it needs to stay below the 6:1 L/D ratio.

Another solution was used by the old British .303 inch Mk VII ball, which had a light-alloy (or other lightweight) tip filler, putting the centre of mass well to the rear.

My intention is not to increase battlefield lethality or range over the 7.62mm M80, but to match them in a smaller and lighter-recoiling package which could also replace the 5.56mm.

I don't see why such a bullet need be any more expensive than the M855A1 or even the M855, which are already complicated bullets to make.

If there is a problem with the range being too long for some places, then the approach already in place for .50 cal (and being developed in 7.62mm) can be adopted: design a training bullet which matches the trajectory of the ball round out to a certain distance, then loses stability and falls to the ground much sooner than usual.

I'm not specifically arguing for the Grendel gun or even the ammo, but for a long-range medium-powered round somewhere in the 6.5-7mm calibre range. The Grendel is currently the closest available round at the bottom end of that range, which is why I'm interested in it: it would make a good test-bed.

[stanc]

It's true that the Norma 120gr FMJ load tested by AA did not begin to yaw until about 7 inches into the gel block.

As for your questions, I'd say:

1. Yes. By using either a two-piece core with lightweight (aluminum?) front and lead rear, or perhaps a design similar to that of the WWII 6.5mm Jap bullet.

2. Maybe. Although substituting copper or other non-lead material may not produce as rapid onset of yaw.

[LR1955]

If there is a problem with the range being too long for some places, then the approach already in place for .50 cal (and being developed in 7.62mm) can be adopted: design a training bullet which matches the trajectory of the ball round out to a certain distance, then loses stability and falls to the ground much sooner than usual.

Tony:

The Training Practice rounds have been done in various forms over the decades and unfortunately it is a very expensive failure, both mechanically and in terms of realism in training.

OK -- if you only want to match 7.62 Ball -- why would you want a VLD?

A true VLD has so many design flaws that it would be an extremely poor choice for any organization that depends on mass produced ammunition and weapons. VLD's are hard on dies and harder to get to shoot well as the shooter must tune the seating depth to suit his individual rifle and this changes as the throat gets eroded. I used to make some true VLD's in .30 caliber and you have big problems with them because they also need to be shot at a pretty specific speed for you to see a difference in any practical terms. This is because with a true VLD you don't have any rounded area before the shoulder of the bullet that the air can flow over easily. It hits a pretty abrupt junction between tip and shank and if that speed is too high or low, you get some severe drag from the tip and that junction. Not a good idea.

Yes, reducing the meplat down to a needle point does increase a ballistic coefficient and the results are impressive when reading them from a ballistics computer. In terms of real use, compared to the open tip match bullets or even a FMJ, it may have meaning to some competitive long range shooters but for military or hunting purposes, it has no meaning aside from perhaps more penetration. Providing the tip isn't bent when it cycles through the weapon and all the tips are made absolutely perfectly.

A hybrid design between a tangent and secant ogive is an option and I would bet the current issued M-80 and 855 use a hybrid design. So, that one is a probable. 123 Lapua, AMAX, SMK are (I believe) hybrid ogives. OK then a 110 - 120 grain 1.2" long 6.5 with a hybrid ogive of 7 or 8 and a boat tail of some length where by the shank is still long enough for mechanical advantage even in barrels that are heavily worn -- probably around 3/10th of an inch.

Now you got to invent a powder that will push that bullet out a 16" barrel at 2700 fps with chamber pressures under 45K and then you will match the issued M-80 but you won't surpass it to any significant degree unless you can hit 2800 or more FPS.

Or, you can issue the guys a 77 grain 5.56 load for their carbines and be done with it.

LR1955

[Tony Williams]

To match the long-range (up to 1,000m) performance of the 7.62 M80, in terms of retained energy and other metrics, with a smaller and less powerful cartridge requires a bullet with a better ballistic coefficient than the M80's. The 123 grain Lapua Scenar seems to do that job very well in the Grendel, so it's a matter of getting close to the BC of the Lapua with a mass-produced FMJ military bullet.

As far as 77 grain 5.56's are concerned, I have the strong impression that no calibre smaller than 6.5mm is likely to prove acceptable as a replacement for 7.62mm, in terms of penetration and terminal effectiveness. The Chinese tried to make a universal cartridge with their 5.8x42 (in light and heavy loads), but their army is hanging onto their 7.62x54R MGs.

[JASmith]

As far as 77 grain 5.56's are concerned, I have the strong impression that no calibre smaller than 6.5mm is likely to prove acceptable as a replacement for 7.62mm, in terms of penetration and terminal effectiveness. The Chinese tried to make a universal cartridge with their 5.8x42 (in light and heavy loads), but their army is hanging onto their 7.62x54R MGs.

Tony, you are probably on the mark with the 7.62 observation. The debates here haven't gone to the level of detail as they have in your Military gun and Ammunition forum. For this reason, not everyone here will instantly concur.

Further, it would seem that there is wisdom to carrying more than one hypothesis forward until at least the time a new cartridge is adopted by one or more significant military. The value added is that, especially if your position is ultimately shown to be the best realizable option. the debate will have shown that and the adoption decision will be more clear-cut.

This would suggest at least one hypothesis that has the 7.62 maintained as the "heavy" and a "light" that is somewhat more capable than the current 5.56 NATO.

One of the "light" options could well be something like the 77gr MatchKing that LR1955 mentioned and that the reporting indicates that it is be liked and respected by the troops using it.

Another might be a larger case in either 5.56mm or 6mm.

[stanc]

One of the "light" options could well be something like the 77gr MatchKing that LR1955 mentioned and that the reporting indicates that it is be liked and respected by the troops using it.

Joe, that doesn't seem like a viable option for Tony's goal. I'm pretty sure that the Brits consider hollowpoints (whether of the fragmenting type, like Mk262, or expanding, like Mk318 and "brown tip") to be in violation of the Hague treaty.

[JASmith]

Joe, that doesn't seem like a viable option for Tony's goal. I'm pretty sure that the Brits consider hollowpoints (whether of the fragmenting type, like Mk262, or expanding, like Mk318 and "brown tip") to be in violation of the Hague treaty.

Stan,

You are correct. The 77 gr Matchking is a place-holder for the longer term solution. A convention-compliant bullet needs to be the core of the discussion. Also, our marksmanship guru points out that bullets of the MatchKing quality are not likely to be manufacturable in the quantities we need. Further, those manufacturing limitations will likely also result in less aerodynamic efficiency. Both the aero efficiency and terminal effectiveness goals push us to longer and heavier bullets with the 77 gr 5.56 being at the low end.

That's part of the reason I mentioned the slightly larger case. We can get the effectiveness of the high quality 77 gr bullet with a somewhat heavier but less efficient cooper-steel bullet driven at the same or slightly higher velocity. I can see this logic pushing us into 6mm...

Remember also that Tony is searching for a universal infantry cartridge to replace both the 5.56 and the 7.62 in infantry roles up to and including the GPMG. He has it right that the 6.5 120+ grain class of bullet is the minimum likely to be seen as a viable 7.62 replacement for the GPMG. Problem is that it stresses the assault rifle role and we still have the vehicle and aircraft-borne 7.62 inventory. The vehicle and aircraft-borne weapons community, given a choice, would likely opt for retaining the 7.62 but enhancing the ammunition.

[Tony Williams]

Remember also that Tony is searching for a universal infantry cartridge to replace both the 5.56 and the 7.62 in infantry roles up to and including the GPMG. He has it right that the 6.5 120+ grain class of bullet is the minimum likely to be seen as a viable 7.62 replacement for the GPMG. Problem is that it stresses the assault rifle role and we still have the vehicle and aircraft-borne 7.62 inventory. The vehicle and aircraft-borne weapons community, given a choice, would likely opt for retaining the 7.62 but enhancing the ammunition.

Yes, that sums it up well, but I'd make a few additional points:

1. The 5.56mm is an unreliable performer (in terms of penetration and terminal effectiveness) even at short ranges, so a bigger and more powerful round would be desirable even if there were no call for a significantly longer range. This is what led to the 6.8mm Rem. So any "ideal" assault rifle round would have more ammo weight and recoil, by definition.

2. The recoil of a rifle with an intermediate round in the 1,800-1,900 ft/lb energy zone (probably the minimum for a "universal" cartridge) doesn't feel much worse than 5.56mm, and feels a lot less than 7.62mm. I say this after firing HK416, HK416/6.8 and HK417 in quick succession. So it should still be controllable in burst fire if needed in a short range emergency.

[LR1955]

Gene:

I don't see any mention of wanting to use a VLD in Tony's posts.

FWIW -- a year or two ago, I asked on the IAA (cartridge collectors) forum about M80 projectile shape, and was informed by one of the knowledgeable individuals that it has a secant ogive.

Stan

Stan:

Tony said "Is it possible to design a low-drag 6.5mm FMJ bullet of around 120-125 grains which exhibits rapid and reliable yaw and upset on impact?"

This implies VLD all the way.

LR55

[LR1955]

To match the long-range (up to 1,000m) performance of the 7.62 M80, in terms of retained energy and other metrics, with a smaller and less powerful cartridge requires a bullet with a better ballistic coefficient than the M80's. The 123 grain Lapua Scenar seems to do that job very well in the Grendel, so it's a matter of getting close to the BC of the Lapua with a mass-produced FMJ military bullet.

As far as 77 grain 5.56's are concerned, I have the strong impression that no calibre smaller than 6.5mm is likely to prove acceptable as a replacement for 7.62mm, in terms of penetration and terminal effectiveness. The Chinese tried to make a universal cartridge with their 5.8x42 (in light and heavy loads), but their army is hanging onto their 7.62x54R MGs.

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

[stanc]

To match the long-range (up to 1,000m) performance of the 7.62 M80, in terms of retained energy and other metrics, with a smaller and less powerful cartridge requires a bullet with a better ballistic coefficient than the M80's. The 123 grain Lapua Scenar seems to do that job very well in the Grendel, so it's a matter of getting close to the BC of the Lapua with a mass-produced FMJ military bullet.

According to Lapua's numbers, the 108, 123 and 139 grain Scenars, and the 144 grain FMJBT, have BCs in approx the same proportion to their weight. If the same length is retained for a 123 grain FMJBT, it should have a BC close to that of the 123 Scenar: 0.527