03-03-2013, 11:41 PM
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.
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.