How could or should the 6.5 mm Grendel be improved?

[Bill Alexander]

So the increase in envelope for this mythical rifle would not then throw you on the weight spiral upward, especially as the recoil is now increased.

I have another question. how much extra velocity, projectile weight is actually required to meet the requirement. Is another 200 fps enough. would 400 fps be better. In which case you will need a much longer casing with more volume and more pressure.

[Guardsman26]

1. Weapon weight issues

A lot of interesting comments. Before I try and address some of the points raised, I’d like to share a story. A friend who is a captain in a certain UK Special Forces unit recently returned from Afghanistan. I asked him about his tour and as you’d expect told me zip. But knowing about my interest in military small arms, we did discuss weapons he had used. Until recently, the Colt Canada C7 / C8 in 5.56 mm was the most common weapon of choice. But not anymore. Most operators have now swapped these for HK417s with 16” barrels. Apparently, they love it. They can shoot out to 600 meters and equally use it in close quarter house clearing. H&K have done a great job damping the recoil so in extreme circumstances, firing automatic bursts isn’t an issue. And, perhaps most important of all, there are no issues with the terminal effectiveness of 7.62 mm ammunition. Ah, I said, but isn’t the HK417 quite a bit heavier than the C7?

The answer was: sure, but the need for range and lethality trumps weight saving. Besides, he said, it’s not as if the HK417 is an order of magnitude heavier than the C7. If you find it cumbersome, mate, get yourself down to the gym! Having used the FN FAL in 7.62 mm (as the SLR L1A1) for seven years, I tend to agree. I also found that most of my soldiers as well as yours truly could shoot accurately to 300 meters with it. So, before we get hung up on weapon weight, let’s focus on the job in hand and what we need to get it done.

2. Projectile first, then weapon

I’ve mentioned that an ideal round needs to match 7.62 mm in a smaller, lighter package. Let’s be more specific. 7.62 mm is effective at 600 meters when fired from an assault rifle. British Army designated marksmen are hitting targets at 800 meters no problem. With the GPMG, gunners are effectively suppressing targets at 1,500 meters. So, if a 6.5 mm Grendel round can match 7.62 mm velocity and retained energy at 600 meters, then it’s on target. In fact beyond that range, thanks to its more aerodynamic bullet, it will overtake 7.62 mm and out perform it at longer ranges. Based on the data I have seen, a 6.5 mm Grendel will only do this in a weapon with a 24-inch barrel.

You don’t need to improve the Grendel much to get it to match 7.62 mm,. According to Tony William’s calculations concerning optimal energy values, my firm belief is that the ideal compromise can be achieved. You need slightly more muzzle energy than the current round generates to match 7.62 mm reliably, not necessarily in an assault rifle, but in a machine gun. The current Grendel cartridge is right at the limit of its capacity and the bullet is long. I don’t see any way of of putting more propellant behind the current 6.5 bullet (which has an almost perfect G7 FF and G7 BC) without slightly increasing case capacity.

You could argue that, actually, you don’t need your GPC to match 7.62 mm. But if you don’t do this the 6.5 mm Grendel only replaces 5.56 mm, not 7.62 mm which would need to be retained to reach out to 1,200 meters - the required range for machine guns.

The strongest argument in favor of the Super G is that it is a viable replacement for 7.62 mm - longer range, lighter weight, lower recoil. And to do all this the optimal cartridge design is probably only slightly longer than the existing 58 mm OAL Grendel 6.5 mm, and nowhere near as long or wide as a .260 Rem, 6.5 x 47 Lapua or 6.5 mm Creedmoor and virtually the same weight as the current 6.5 mm Grendel.

I agree with LRRP52, you don’t want a weapon with a chamber pressure of above 60,000 psi. The M855A1 is running at proof testing limits. That’s another reason to use an extended case.

3. The weapon

The ideal weapon could well be an AR12.5 - something in between the AR10 and AR15. If such a weapon were developed the optimal design could be an AR15 with an extended and strengthened receiver or a lightened AR10. Either way, you end up with a rifle that weighs in between an AR15 or AR10. (BTW, the Lewis Machine Tool 7.62 mm AR10-based DMR bought by the British Army as the L129A1 is lighter than the L85A2 SA80 assault rifle.) The FN SCAR-H firing a 6.5 mm round would have very little extra weight penalty versus the FN SCAR-L in 5.56 mm.

The real weight saving is not so much in an assault rifle but in a light machine gun. A 6.5 mm version of the 7.62 mm Minimi could reduce the weight to around 7 kg. As I think I mentioned elsewhere, when it comes to ammo, a weight saving of 30% when you’re carrying 2,000 rounds of link isn’t insignificant.

One thing I can’t make-up my mind about is the overall form factor of the ideal cartridge. With the US 6 mm SAW and UK 6.25 mm rounds, the designers opted for very long slender cartridges. This meant that you could fit 30 rounds in a 7.62 mm magazine. For this reason, I thought an extended 6.8 mm Rem case (.30 Rem) might be a better option than the 7.62 mm x 39. As Stan C points out, the difference in a 5.56 mm magazine is about 25 rounds of Grendel versus 28 rounds of 6.8 Rem.

4. To summarise

I think Tony Williams has summed up the GPC requirement better than most: caliber of around 6.5 to 7 mm, MV of 800-900 mps, 7-8 gram (107-123 grain) projectile. Same retained energy as 7.62 mm at 1,000 meters. To achieve that with an 8 g / 123 gr projectile you need a case capacity nearer to 40 grains of water rather than the current Grendel's 30.

Bill A, you understand this better than most. I'd love to see you develop a Super-Grendel using an extended 6.8 mm case. The only real problem you'd have is figuring out what to call it.

[JASmith]

Guardsman -- you should read up on wound ballistics and penetration mechanics before insisting on equal energy. I know that Tony and many others like this metric but it has no grounding in wound ballistics or penetration mechanics.

More appropriate metrics are likely momentum density for penetration and energy density for breaking hard plates.

As you and others have pointed out many times, we have to count on tumbling for effective wounds as a result of political constraints. This means that the bullet length is the measure to look at. In this regard, 110 to 130 grain 6.5 mm bullets are long enough.

The Grendel is very close to matching or exceeding the M80 round in these metrics when using equal barrel lengths at 1000 meters and exceeds it at longer ranges.

The velocity data comes from the 50,000 psi operating pressure imposed by the desire to have very long bolt life.

Further, the 5.56 experience tells us that one can do even better with steel-tipped bullets when it comes to breaking through plates.

So, let's look at what is doable with bullet design and powder formulations within the constraints of the current design. Bullet design to look at military-production realizable ballistic coefficients and 'green-compliant' penetration optimization. Powder formulations to get best velocity in barrels consistent with shorter barrels.

You have already indicated that the 7.62x51 works fine in 16" barrels. The performance of the cartridge should be the norm to meet or beat.

[stanc]

As Stan C points out, the difference in a 5.56 mm magazine is about 25 rounds of Grendel versus 28 rounds of 6.8 Rem.

No, no, no, no, no! The actual difference is 25 rounds of 6.5 Grendel versus 26 rounds of 6.8 SPC, tops! At best, that's one round advantage to the smaller case diameter, not three!

This is easily calculated. A 25-round, staggered column magazine has one column of 12 rounds, and a second column of 13 rounds.

13 x 0.44 = 5.72 inches
13 x 0.42 = 5.46 inches

Difference = 0.26-inch, which is less than the 0.42-inch diameter of the 6.8 SPC case. Maybe sufficient for 26 rounds capacity, but not 28 rounds.

[Guardsman26]

JAS,

The wounding mechanism has to do with bullet construction as much as shape. One issue with 7.62 mm NATO is that it doesn't yaw rapidly in soft tissue. Of course, it doesn't need to, because it makes a pretty large hole without upsetting.

I am not relying on velocity and retained energy to achieve terminal effectiveness, but rather construction. As I mentioned, I favor lead-free not because of the absence of lead but because of the addition of steel. Steel penetrates very well, but it has also to yaw in soft tissue.

If the Grendel upsets more rapidly and more reliably, then, yes, you could be right: a GPC wouldn't need as much energy as 7.62 mm. I haven't seen any gel tests with Grendel, so if anyone can provide data on how an FMJ Grendel performs in soft tissue, then I'd be interested to see it. So is, M855A1 - but no one else in NATO is using it due to stricter interpretation of Hague / Geneva Conventions.

Stan C,

Thanks for correcting me on that.

[stanc]

[The Grendel is very close to matching or exceeding the M80 round in these metrics when using equal barrel lengths at 1000 meters and exceeds it at longer ranges.

Only when comparing a 6.5 match HPBT to M80, but not when comparing a 6.5 FMJ to M80.

[Bill Alexander]

If you push both weapon and also ammunition envelope then you find that the approximation is so close to the existing 7.62 as to make the effort academic. Longer ammunition will demand the envelope for the bolt to travel now matches the 7.62 so any weight saving is negated for the weapon. So too does the now long ammunition require both case and projectile weight so the savings basically disappear. I am currently working on a 338 semi auto and the effort to remove a 1/2" of length from the receiver is a substantial weight saving.

In the instance were weight is secondary to performance as stated, and the soldiers solution is to spend more time training, then the consultants are now truly tilting at windmills. You already have the solution but quest not to find it but to invent reasons for your existence.

I have posed two questions in this thread. The first is for a definition of what the performance should be. Not in respect to "well like a 7.62" but actual hard numerical requirements in terms of range, lethality and target definitions. What do you want it to do? In the absence of the question are we to find the answer is indeed 42?

The second is that if 200 fps can be justified as the increase required, how can 400 fps be excluded. Why does a 7.0 g projectile make the cut but you can already disregard a 9.0 g projectile. This question in effect mimics the first, but then poses the question that perhaps the proposed long 6.8 will also fall short.

Given the number of cartridges that currently fit the package needs, starting at the 6.5 Grendel and progressing through the 6.5x47, 6.5 Creedmore to the 260 Rem, 7-08 and finally the 7.62 with variations on either side both in case diameter (Italian) and also length (BR types) The pursuit of the one we do not have but that overlaps perfectly with another seems odd. Perhaps a 7mm BR or 7mm Creedmore would be a better initial platform buried in the confines of a 417. Lot less development and debate. Problem solved now man up and carry it.

[stanc]

I haven't seen any gel tests with Grendel, so if anyone can provide data on how an FMJ Grendel performs in soft tissue, then I'd be interested to see it.

Norma 120gr FMJ:



Penetration ~7 inches before onset of yaw. Somewhat inferior to Fackler's wound profile drawing of M80.

[LRRPF52]

Bill makes a valid point, and one that has been brought up here over the years: Without a specific requirement, we're not even chasing moving goal posts. There isn't a defined playing field.

Basing an army's service carbine selection on some of the preferences of marginal units who have entirely different mission profiles, with insane amounts of support behind them compared to conventional units, isn't a sensible approach. If you are doing a direct action raid, with helo insertion and extraction, you can go in with minimal kit and a basic load minus. 5 mags is usually more than enough to get it done for an SF team, with a few to hold off any contingencies if things get nasty and you need an immediate exfil.

For joe tentpeg in the line, who doesn't have that kind of helo or priority CAS support, (5) 20rd mags might get him through one contact, with a mag or two to die in-place or wait for relief, taxing the system. We all tried that (US, British, Germans, etc.), and it just doesn't cut the mustard for units that need to be able to continue mission after contact.

Negative again. You don't need a 24" barrel to get the 6.5 Grendel to do what you want. 16" is more than plenty. I'm not making this up. It doesn't take a lot to get a 16" Grendel to push 123gr projectiles at 2600fps. I've had factory ammo that clocked 2583fps out of mine with a commonly available powder, not a purpose-built powder. With a stronger bolt and extension, you can run the pressures at 55,000psi and use an industrial powder specifically designed to meet the unspecified requirements that nobody has mapped out yet.

You don't need more capacity, just the right powder. We already have guys who have used Hodgdon's CFE to push 130gr Norma Golden Targets at 2700fps with just a slightly longer COL from modified polymer mags.

The wounding mechanism has to do with bullet construction as much as shape. One issue with 7.62 mm NATO is that it doesn't yaw rapidly in soft tissue. Of course, it doesn't need to, because it makes a pretty large hole without upsetting.

Velocity is the biggest wounding mechanism, combined with bullet construction. A thin jacket with lead core will fragment above a certain velocity threshold. Once it falls below that, you then have to rely on construction. Yawing may or may not happen depending on tissue integrity, anatomical landmark penetration angle, and internal anatomical arrangement along the wound channel.

Let me reinforce that no longer case is needed than what we have already. Projectile weight, construction, and velocity can only be addressed once we have a specific set of requirements. Do you go 100gr solid sectional bullet for an assault rifle/dual-purpose load at 2950fps? Do you go with a 130gr LMG load at 2700fps designed to penetrate? Without any specific requirements, we're spinning wheels.

There are existing loads that will fill the DM role that the UK is currently using the L129A1 in, but that adds another caliber to the system. I've also played with the L85A2, and the 16" LMT is a beast compared to it. The extra 4" of barrel that needs to be 1.25" dia. adds a ton of weight to that pig of a carbine.

[Michael]

Bill and LRRPF52 have some very valid points - the main one being what is the requirement - or what will become the 'MilSpec' for this new rifle/cartridge?

Several years ago, I was part of the team that looked at Personal Defense Weapons (PDW) for the Marine Corps. As I remember it, there was no talk in the requirements for a specific bullet weight, caliber or velocity. We were focused on accuracy at 100m, penetration/damage in gel, and penetration of body armor type X (cannot remember what type we wanted to penetrate), weight/size of system, ammo capacity and weight of ammo, and modularity of the system/ability to accept current optics/accessories. Purpose of the PDW was to replace the M9 for vehicle drivers, aircrew, and armored vehicle crewmen with a weapons system more capable than the M9, yet smaller than the M4/16.

The other focused area we looked at was what would be the suitability of anything we recommended for the future - theaters other than Iraq/Afghanistan. None of us on this team was SpecOps, nor were any of us competition shooters. We all had some combat experience, and came from a variety of specialties. We all realized to get the corporation to buy off on our recommendations, we needed to show utility in all military applications, current and future, and get buy in from all parts of the corporation – not just the combat arms folks. This is the same tact that would need to be taken for – I would assume – any military small arms procurement.

[JASmith]

Well stated Michael!

We could proceed by positing requirements along the lines you describe, or we might be able to encourage Guardsman26 or anyone else to bring forward a public version of an existing requirement.

If one exists, we can rather quickly determine how well the Grendel or any other cartridge satisfies it.

[Guardsman26]

If you push both weapon and also ammunition envelope then you find that the approximation is so close to the existing 7.62 as to make the effort academic. Longer ammunition will demand the envelope for the bolt to travel now matches the 7.62 so any weight saving is negated for the weapon. So too does the now long ammunition require both case and projectile weight so the savings basically disappear. I am currently working on a 338 semi auto and the effort to remove a 1/2" of length from the receiver is a substantial weight saving. Look, we're talking about a weapon in between the AR10 and AR15 in weight. With a modern assault rifle design like the SCAR-H in 6.5 mm, the weapon weight increase is negligible.

In the instance were weight is secondary to performance as stated, and the soldiers solution is to spend more time training, then the consultants are now truly tilting at windmills. You already have the solution but quest not to find it but to invent reasons for your existence.That's a cheap shot, so forgive me for not bothering to respond to it..

I have posed two questions in this thread. The first is for a definition of what the performance should be. Not in respect to "well like a 7.62" but actual hard numerical requirements in terms of range, lethality and target definitions. What do you want it to do? In the absence of the question are we to find the answer is indeed 42? You should know what the requirement is, Bill. You were at the same Government meeting that defined it. That's why industry is looking at this topic. Confidentiality prohibits revealing the exact nature of the requirement, but using 7.62 mm performance as a benchmark and setting out to create a VLD projectile that matches it in the lightest possible package is actually pretty succinct description of what is needed. Moreover, it allows plenty of scope for creativity. You will also be aware that at the same meeting it was expressed that the existing 6.5 mm Grendel was not considered suitable for military use in both assault rifles and machine guns, nor a close enough match for 7.62 mm when FMJ projectiles were used. PM me if you'd like me to jog your memory.

The second is that if 200 fps can be justified as the increase required, how can 400 fps be excluded. Why does a 7.0 g projectile make the cut but you can already disregard a 9.0 g projectile. This question in effect mimics the first, but then poses the question that perhaps the proposed long 6.8 will also fall short. It's simple, a 7.0 g projectile is probably the heaviest bullet you'll get in a lead-free 6.5 mm based on existing VLD design. If you can manufacturer a heavier lead-free bullet, then great. The requirement for lead-free is not mine, but a Big Army one. No new round is likley to be accepted unless it is so constructed. Besides, if you use a slow shooting heavy 123 gr 6.5 mm round, you end up with a significantly higher trajectory than either 7.62 mm NATO or 5.56 mm NATO

Given the number of cartridges that currently fit the package needs, starting at the 6.5 Grendel and progressing through the 6.5x47, 6.5 Creedmore to the 260 Rem, 7-08 and finally the 7.62 with variations on either side both in case diameter (Italian) and also length (BR types) The pursuit of the one we do not have but that overlaps perfectly with another seems odd. Perhaps a 7mm BR or 7mm Creedmore would be a better initial platform buried in the confines of a 417. Lot less development and debate. Problem solved now man up and carry it. Sorry, Bill, but I would argue that no current round fits the requirement. Your round isn't quite a ballistic match for 7.62 mm, although it comes close. The 6.5 mm x 47 Lapua, .260 Rem and even Cris Murray's 6.86 mm UIAC are, in fact, all better than 7.62 mm. The problem is they are much better than 7.62 mm than they need to be, so weigh more and are around the same size. We want equal performance in the smallest possible package.

My question is a very simple one: how should the 6.5 mm Grendel be improved. You're saying it's fine as it is. Fair enough, but so far no NATO or Western Army has adopted it. And it's been around for quite a while. What you achieved with the Grendel is amazing. I'm definitely a fan. I believe it deserves a wider audience, that's why I started this thread.

[JASmith]

We been through this hoop before.

The previous debates along this line eventually died or were shut down because too many people insisted on arguing performance base on vague performance factors like those described here. The lack of specificity implied by "better than 7.62x51" leaves too much room for comments like "need 200 ft/sec" more.

We need to see some numbers that define the problem.

Further, requiring the same velocity or energy at distance completely ignores the mechanics of the business.

Hence the numbers need to define what the acquisition community is asking for even if some sanitization is done.

We need to use terms along the lines of "minimum acceptable" and "desired level" in stating this. Demanding equal or better to the 7.62x51 at range is absolutist and not consistent with good acquisition policy.

If this sounds repetitive, scroll back up through this thread and a pattern of repetitiveness will emerge.

[stanc]

Stan C, Thanks for correcting me on that.

You're welcome. I'd like to further suggest that, with no more than a one round difference in magazine capacity, the 6.5 Grendel case may be a better choice than the 6.8 SPC case. This is due to the weight and performance goals you seek.

Ammo Weight: IIRC, the Grendel case is slightly (~10 grains?) lighter than the SPC case. That's not much, but every little bit helps.

Weapon Weight: If new rifles and machine guns are designed to fit the cartridge, the shorter Grendel case would permit shorter -- and therefore slightly lighter -- weapons to be developed.

Ballistic Performance: As I understand it, a short, fat case allows better powder combustion than a long, slender case, thereby giving a slight edge to the Grendel case.

[cory]

Guardsman26 so there are defined requirements in the government realm. Which government are we talking UK, USA, combination of the two, NATO? I fully understand there's only so much you can say. What governments were in the meeting you mentioned?

Let me ask you this which is more of a priority the Grendel exceeding 7.62 terminal effectiveness or barrier penetration at 1000 yards?

I take it from your post that the gov. you've been talking about has done test with the Grendel firing a FMJ. Is there anything in those results you could share?

The current requirements we have are replace multiple military ARs, LMGs, DMRs and multiple military rounds with a single AR, LMG, DMR using a single FMJ round.

What we need is John Galt to design us this mythical beast as he designed the engine which converts energy from atmospheric static electricity.

Please don't take that remark at a shot at you or anybody, but to put the military wishlist into perspective.

Correct me if I'm wrong, but as it sits the Grendel can exceed 7.62 performance with the right round.

I believe these are the only two feasible options and I ask this from a Grunt perspective, which is the more ideal scenario the grunts being supplied two calibers with FMJ rounds and issued multiple ARs, LMGs, and DMRs that will all individually excel in their respective environment or is it more ideal to issue the grunts one AR, LMG, DMR, and caliber with each platform receiving a round specifically designed to compliment the platform while operating sufficiently in all platforms?

I understand the multiple rounds is a logistic nightmare, but is the current situation not a logistic nightmare two calibers with multiple rounds for each caliber? Either way this goes logistics is going to having multiple rounds to deal with. I propose we assume logistics is not a factor and continue this exercise to benefit the grunts understanding that logistics won't get their ideal scenario without drastically compromising the lethality of the grunts.

What's worse case scenario of one caliber of AR, LMG, DMR, and multiple rounds. The DM is only able to fill his magazines with AR rounds? Let us not forget that the SAWs ability to accept a 556 mag was a huge advantage in its favor.

That being said if anything needs to be improved I'd suspect it'd be the bolt. Not so that the AR round can be pushed beyond 50ksi, but so that the AR can utilize the LMG and DMR round if necessary.