How could or should the 6.5 mm Grendel be improved?

[Buck2732]

Gdsm62 Is that not reinventing the 6.5x47 Lapua. Or am I missing something?

[JASmith]

The 6.5x47 base diameter is the same as the one for the 7.62X51 NATO, so there is no gain in rounds in the magazine.

The Grendel has the same base diameter as the 7.62x39 Russian, so the Grendel enjoys about as good a magazine load out as rifles chambered for the Russian round.

[Guardsman26]

Gdsm62 Is that not reinventing the 6.5x47 Lapua. Or am I missing something?

That's a very good question.

The 6.5 mm x 47 together with the .260 Rem and 6.5 mm Creedmoor are all excellent rounds. In fact, they quite comfortably exceed 7.62 mm in a package that shoots flatter, faster and with less recoil. As JAS points out, they're the same weight and size as 7.62 mm NATO, so may not offer a sufficient increase in overall capability to justify the effort of switching.

What we would ideally like is 6.5 mm x 47 performance in a 6.5 mm x 39 package. Sadly, that dog just won't hunt. Therefore, what I'd like to see is something in between.

The 7.62 mm x 39 case is an ideal start point for an intermediate round. But if an extended 6.8 mm x 45 case were used instead, the round would have an even smaller diameter allowing more to be fitted into a standard magazine.

[JASmith]

...But if an extended 6.8 mm x 45 case were used instead, the round would have an even smaller diameter allowing more to be fitted into a standard magazine.

The 6.8x45 case is too long for the kind of bullets we would need for long range effectiveness in a 6.5 when we keep the length short enough to operate in the AR-15 class of rifles.

It would, however be very interesting when taking advantage of the length provided by the AR-10 magazine well.

That raises the question of ground rules for this new cartridge. Are we restricting to the AR-15? Are we allowing AR-10 rifles? Or, are we assuming an entirely new rifle?

I know that much of this material was covered in Tony Woilliams' MG&A forum a couple or three years ago. It seemed that the group converged on something like a modern version the 6.5mm Carcano with cartridges derived from the 25 & .30 Remington running a close second. That discussion presumed a new rifle design optimized around the cartridge.

The ground rules will make a difference in both the optimization path and the feasibility argument.

[Von Gruff]

I am reluctant to intrude in this very interesting discussion because I have no military experience and dont even have AR experience --but my 6.5 Gm with 21 in barrel easily takes the 100gn TTSX tp 0ver 2925fps, the 123 gn A Max to 2700 and the 129gn Interlock to 2550 in Lapua fireformed 7.62x39 brass. About all I would like to see with this brass is a little better neck length as when FF I get a case length of 1.5 so another .02-.03 would be good. COAL with the TTSX is 2.380, with the A Max at 2.405 and the Interlock is at 2.320 and I know Sneaky One has his AR magazines except over 2.3 so somewhere there has to be a combination of these paremeters (with adjustments of throating and COAL) that might come within the requirments you are all talking about.

[stanc]

The 7.62 mm x 39 case is an ideal start point for an intermediate round. But if an extended 6.8 mm x 45 case were used instead, the round would have an even smaller diameter allowing more to be fitted into a standard magazine.

According to my calculations, if we're talking about a 25-rd magazine, the difference in capacities would be no more than one round, at most, and maybe zero rounds. That doesn't seem significant to me.

[LRRPF52]

I am reluctant to intrude in this very interesting discussion because I have no military experience and dont even have AR experience --but my 6.5 Gm with 21 in barrel easily takes the 100gn TTSX tp 0ver 2925fps, the 123 gn A Max to 2700 and the 129gn Interlock to 2550 in Lapua fireformed 7.62x39 brass. About all I would like to see with this brass is a little better neck length as when FF I get a case length of 1.5 so another .02-.03 would be good. COAL with the TTSX is 2.380, with the A Max at 2.405 and the Interlock is at 2.320 and I know Sneaky One has his AR magazines except over 2.3 so somewhere there has to be a combination of these paremeters (with adjustments of throating and COAL) that might come within the requirments you are all talking about.

Your real-world results with a Grendel chambered in a bolt gun are what I've been trying to tell some of the new members to the discussion about increasing the velocity of the Grendel. The only real thing you need to push the case to what it will handle is a stronger bolt. You could extend the COL a tiny bit, but I don't think it's necessary.

You will not get 6.5x47 Lapua performance from a shorter cartridge with a smaller diameter base, and an assault rifle or machinegun should never be run at 6.5x47 Lapua pressures in that bore diameter.

When we start talking about going back to a battle rifle-sized weapon, we have failed the soldier, the mission, and the logistics chain. You want to know what to do to improve the 6.5 Grendel?

Shoot thousands of rounds through it. Any increase in powder capacity will not be able to be exploited by well over 95% of Infantry Soldiers, and the few that can will not see a practical difference at distance anyway.

[JASmith]

My experience with previous discussion on this topic as well as in actual weapons concept definition suggests that we need to establish ground rules for comparisons. In this regard, I'm not clear on what the "new" cartridge is expected to do.

1. Match the 7.62X51 at 1000 meters?
   
2. Same barrel length, or a 16" 'new' and a 20" 7.62x51?
   
3. What does 'match' mean?
   

For example, if you want lethality to be the same, does that include probability of hit with one shot, or with a magazine load?

I know that this series of questions appears to move in the direction of complexity, but the restraints are needed. The alternative is akin to wrestling a bunch of pythons all at once. We can spend tens of posts on one item of performance with only to find that the OP had a different metric in mind than poster B, and Mr C has an entirely different one. This leads to confusion, frustration, untoward comments, and no convergence on a common solution.

If we are talking about wounding potential, we know that kinetic energy is one of the poorest metrics one can choose. This begs the question of what metric to use.

[adrenaline junkie]

I think a "Super G" defeats the purpose. There's already the 6.5 Creedmore and the 260 Rem which would be an even easier swap because it's based of the 7.62x51, and would already have more power than a slightly lengthened Grendel.

[stanc]

I think a "Super G" defeats the purpose. There's already the 6.5 Creedmore and the 260 Rem which would be an even easier swap because it's based of the 7.62x51, and would already have more power than a slightly lengthened Grendel.

Easier, yes, but also more powerful than deemed necessary, as well as heavier and bulkier than acceptable.

The goal is a cartridge that achieves the desired performance, without excessive weight and bulk. A "Super G" would accomplish that end; 6.5 Creedmoor and .260 Remington would not.

[ricsmall]

Anyone thought about the concept of Olympic arms UMAR lower? It's a standard ar15 lower with the mag well machined out for a larger magazine. It works for the 22-250, I don't know about combat feasibility, but it works for civvies. I've pondered it for my extremely long throated Grendel. Just a thought.

[adrenaline junkie]

A super g thats 10-15% longer is only a couple mm shorter than the other two, in a weapon that is much larger. (Ar10 vs ar15) I dont think a new cartridge would be any benefit. A weakened 260/6.5cm in the same gun is losing power at the same weight.

[LRRPF52]

All that is needed for more performance is a stronger bolt/barrel extension. The case will handle 62,000psi already, but do you really need or want to run weapons at 62,000psi in high volume? To get 100-200fps more mv, is it really worth it? What does 200fps mv give you over current mv, before a military powder has even been developed and tested under the current constraints?

[stanc]

A super g thats 10-15% longer is only a couple mm shorter than the other two, in a weapon that is much larger. (Ar10 vs ar15)

Ideally, it would be "AR12.5" vs AR15. Somewhat larger, certainly, but not as much weight and size penalty as AR10 vs AR15.

[KentuckyBuddha]

Grendel is the norse monster that goldilocks chose just the way it is!

I chuckled at AR 12.5, I may steal this as my own...sorry.

[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.