How could or should the 6.5 mm Grendel be improved?

[stanc]

As for loadout weight, what is the Grendel cartridge weight currently vs .308? And 70% using which version of 7.62x51, M118? or ?

Compared to M80 Ball. The main concern is weight of machine gun ammo.

I lost all of my notes and reference data when I moved last November, so the following is from (possibly faulty) memory.

6.5 Grendel (100gr bullet) = 255gr
7.62 NATO (147gr bullet) = 392gr
_______________________ 65%

Of course, that doesn't include weight of the links.

[stanc]

I am not exactly sure at present. The result will stem from the target definition and the hit probability ie the required carried kills.

Gut says maybe a 6.5 but i would prefer a 7. Keep the OAL short and then work back to the case volume for the optimum operating pressure at an acceptable fill level with the new powders.

That sounds reasonable. In the absence of test data that shows 6.5 would deliver adequate terminal performance, I'm inclined to think 6.86 or 7mm might be necessary. However, that's just a gut feeling.

[Trooper]

I am not exactly sure at present. The result will stem from the target definition and the hit probability ie the required carried kills.

Gut says maybe a 6.5 but i would prefer a 7. Keep the OAL short and then work back to the case volume for the optimum operating pressure at an acceptable fill level with the new powders.

Grendel in the legacy M4 runs at too low a pressure to best utilize the case. I would want to push this up. The technology for this is simple and the bolt/barrel extension geometry is not a problem. The extension/barrel interface might need some massaging to hold up at elevated temps. In a new rifle this is easy stuff and the weight spiral is non existent as long as the mag length is constrained.

The 7mm UIAC is too much like the .280 British (7x43). While I like the 7mm, it does have more recoil (heavier bullet) than the 6.5mm. The one thing that is coming out from my research is that the 6.5mm is at the optimum point among calibers. It has the sweet spot in terms of BC and sectional density. While the 6.5 and 7 are not the best with respect to magnum calibers (too much barrel wear), they are great when comparied to the 7.62x51 or the .30-06. We have the 6.5x55 Swede as the baseline. If we take the .260 Remington (6.5mm-08 with a 140gr bullet) in comparison to the 7mm-08 (162gr) or the 762.x51 (192gr), the 6.5mm comes out strong. It gives similar down range performance with far less recoil.

This whole question would have been moot had the US gone with the .280 British and the FAL back in the '50s!

[stanc]

The 7mm UIAC is too much like the .280 British (7x43).

Actually, it has little in common with the .280 British, which had a long, streamlined bullet and short, fat case. A more accurate comparison is to the .270 British (7x46).

While I like the 7mm, it does have more recoil (heavier bullet) than the 6.5mm. The one thing that is coming out from my research is that the 6.5mm is at the optimum point among calibers. It has the sweet spot in terms of BC and sectional density.

However, 6.5mm lead free bullets may not have sufficient mass for the terminal effects required of a GPMG.

This whole question would have been moot had the US gone with the .280 British and the FAL back in the '50s!

Nah. The 5.56x45 cartridge and M16 rifle would still have been developed and fielded, for the same reasons they originally were. So we'd still find ourselves in the same situation as now, at least with respect to rifles and carbines. But, let's not get sidetracked into a futile discussion of what coulda, woulda, shoulda happened.

[bwaites]

The 7mm UIAC is too much like the .280 British (7x43). While I like the 7mm, it does have more recoil (heavier bullet) than the 6.5mm. The one thing that is coming out from my research is that the 6.5mm is at the optimum point among calibers. It has the sweet spot in terms of BC and sectional density. While the 6.5 and 7 are not the best with respect to magnum calibers (too much barrel wear), they are great when comparied to the 7.62x51 or the .30-06. We have the 6.5x55 Swede as the baseline. If we take the .260 Remington (6.5mm-08 with a 140gr bullet) in comparison to the 7mm-08 (162gr) or the 762.x51 (192gr), the 6.5mm comes out strong. It gives similar down range performance with far less recoil.

This whole question would have been moot had the US gone with the .280 British and the FAL back in the '50s!

AND it ALL would be a moot point if we had gone with a .276 Pedersen before WW2!

[Von Gruff]

The options are quite markedly different.

[BluntForceTrauma]

However, 6.5mm lead free bullets may not have sufficient mass for the terminal effects required of a GPMG.

I'm hoping that by the time we get in a Real Big Shooting War that the adults will be back in charge and they'll be more focused on gettin' the job done than with appeasing the Sierra Club.

John

[Tony Williams]

A 6.5mm lead-free bullet could weigh 7 g (108 grains), maybe a bit more. That's 75% more than the 4g M855, while the 9.5g 7.62mm M80 weighs only 35% more than the 7g. So even if all else is equal (unlikely, given the very ordinary performance of the M80), the lead-free 6.5 should be very much closer in effectiveness to the 7.62mm than to the 5.56mm.

[JASmith]

It turns out that a 62gr 5.56mm bullet scaled to 6.5mm is very close to that weight. That suggests scaling the current 5.56 up to 6.5 could form a basis for assessing the Grendel. The steel core makes a difference in thin armor defeat making the scaling even easier.

I haven't recently run the ballistics numbers, but will soon.

I know that some advocate tests before making claims but we need to do the analysis in order to drum up enthusiasm for testing.

[stanc]

A 6.5mm lead-free bullet could weigh 7 g (108 grains), maybe a bit more. That's 75% more than the 4g M855, while the 9.5g 7.62mm M80 weighs only 35% more than the 7g. So even if all else is equal (unlikely, given the very ordinary performance of the M80), the lead-free 6.5 should be very much closer in effectiveness to the 7.62mm than to the 5.56mm.

I agree. However, the yet-to-be-answered question is, will it be close enough?

[LRRPF52]

In conversation with those who have actually used the new M855A1 barrier blind ammo, it seems to be well-received, with noticeable terminal performance differences that warrant its use. That's even from 10" guns.

The 77gr SMK from the Mk.262 works well on people, but has extremely poor barrier penetration, as it comes apart so quickly.

For Afghanistan, 5.56 weapons are good for clearing mud huts, and that's about it for an entry-level soldier skill set. As mentioned above, for any engagements in the hills, 7.62 NATO is the bare minimum that will even begin to reach out and be effective.

Training is a huge factor in this that can extend the effective range of 5.56 NATO, and I know guys who felt strongly about it being effective out to about 450m from someone with a lot of trigger time behind the guns, to include putting guys down with M855 from an M4A1 through an AK chest harness, but using 3-4 rounds to do it. That is from guys with an extreme margin level of proficiency above the 95th-99th percentile of combat arms soldiers, being that they were in either Tier 1 units, or trained DM's/Snipers, with the optics and wind-reading skills necessary for making 1st-round hits on vitals.

[Michael]

Aren’t the Barnes’ line of bullets lead free? I would think, based on the description, that the 120gr TAC-X would be comparable to the SOST/barrier blind rounds. Would that round not be a starting point for a military purposed round?

Am I off base on this?

[Guardsman26]

I agree. However, the yet-to-be-answered question is, will it be close enough?

Reviewing some of the interesting posts on this thread. I think I asked the wrong question.

Perhaps, I would have made life easier for myself if I had asked: what could be done to help military and LE users accept and use the 6.5 mm Grendel more widely?

The supplementary question is: is it good enough as is? If not, what could or should be done to improve it.

Of course, I stand by three comments:

1. We're not going to replace 5.56 mm any time soon, so don't bother trying
2. 7.62 mm is making a reluctant comeback across NATO - I say reluctant, because the very weight and recoil issues that led to 5.56 mm NATO supplanting it in 1979 have come back to haunt us
3. 6.5 mm is proving itself to be a very accurate and reliable caliber so is an ideal option to be an intermediate cartridge that is genuinely capable of replacing 7.62 mm
4. To actually replace 7.62, a 6.5 mm cartridge has to be as close a ballistic match for 7.62 mm NATO as possible while offering reduced weight and recoil (I am not sure what level of weight reduction triggers NATO excitement)

The 6.5 mm Grendel already comes very close to 7.62 mm across its performance envelope. One potential issue is that existing FMJ projectiles don't yaw rapidly in soft tissue. The same is true for 7.62 mm - of course, 7.62 mm doesn't need to yaw to deliver a fairly extensive lethal effect. That may also be true of the 6.5 mm Grendel given its increased energy versus 5.56 mm.

There is no reason why the construction of the Grendel couldn't be improved to make it yaw sooner in soft tissue, then even a 7 g one should be a very close to 7.62 mm in both retained velocity and energy as well as terminal effectiveness.

One of the issues I've touched upon but probably need to mention in more detail is the need for a tracer round. Would a 6.5 mm Grendel tracer need to be much longer than the existing bullet to give it the extra mass it needed to match the ball round? And if so, would this reduce case capacity and thus the rounds power.

Bill A., where are you on Grendel tracer?

It has also been mentioned using high-power propellant to give the projectile increased velocity and energy. This is interesting anyone like to suggest what the impact might be on MV.

[stanc]

SOCOM reportedly makes limited use of the Barnes TSX, but it's very unlikely that any army will field a solid copper bullet for general purpose ball ammo.

The Scandinavian lead free 5.56 and 7.62 rounds are FMJ w/2-piece steel core, and the US M855A1 and M80A1 have steel tip and copper slug in a gilding metal jacket.

[stanc]

Reviewing some of the interesting posts on this thread. I think I asked the wrong question.

Perhaps, I would have made life easier for myself if I had asked: what could be done to help military and LE users accept and use the 6.5 mm Grendel more widely?

LE probably would not switch until after the military did.

IMO, to make 6.5 Grendel more appealing to the military would require:
- Demonstrating terminal effects equal or better than 7.62x51
- Demonstrating that a Grendel machine gun is feasible

The supplementary question is: is it good enough as is? If not, what could or should be done to improve it.

It needs some projectiles developed that are required for military use, primarily Ball and Tracer.

One of the issues I've touched upon but probably need to mention in more detail is the need for a tracer round. Would a 6.5 mm Grendel tracer need to be much longer than the existing bullet to give it the extra mass it needed to match the ball round?

It would undoubtedly be longer, but precisely how much so, I don't know. Suggest comparing the 120gr 6.5x55 Tracer bullet with the 120gr Norma FMJ to give a close approximation.