Grendel as a Universal Infantry Cartridge

[JASmith]

Gosh, it's good to see this forum again!

Might as well start with an old Grendel topic -- how well it might serve as a universal cartridge for one or more nation's services.

I'd like to call your attention to these articles:

1. The "6.5 mm and the Politics of Procurement" at http://forums.delphiforums.com/autog...ges?msg=4491.1
2. "Grendelmania" -- series of notes at http://shootersnotes.com/grendelmania/
3. The "Battle Rifle Series" at http://shootersnotes.com/battle-rifle-cartridge/

The "6.5 mm and the Politics of Procurement" explores a replacement of both the 5.56 and 7.62 NATO rounds on a likely new platform sometime in the next 5-10 years. The discussion narrows down to a cartridge that looks like a stretched 6.8 SPC. (Be forewarned -- there were 215 posts as of the writing of this note, but the rate is slowing - likely from exhaustion!)

The Grendelmania series uses the military potential as background to focus on Grendel as a medium to large game hunting cartridge.

The "Battle-Rifle" series explores alternatives with a promising candidate that may be viewed as part of the Grendel family.

The principal difference between the Military Guns and Ammunition debate and the ShooterNotes Battle-Rifle discussion is in the assumed long range lethality requirement. One specifies that the resulting cartridge be at least as lethal as the 7.62 mm M80 round at 1100 meters. The other requires that the lethality at 600 meters be at least equivalent to the muzzle performance of 5.56 M855. Similarly, one is aggressive with assumed ballistic coefficients and the other is conservative.

I am of the opinion that the Grendel community can illuminate this debate. Let's look at these questions:

1. Is there really a need for a new military cartridge? Opinions vary widely -- and an informed discussion of what is 'good enough' may be highly useful.
2. Assuming the need exists, what platforms (AR15, AK, AR10, etc.) should the new cartridge be compatible with? The choices make a major difference in cartridge design flexibility, weight, and performance potential
3. What should be the round be capable of and at what range? Remember, this is being viewed as a cartridge capable of fulfilling the medium machine gun role!
4. What are the viable technical alternatives -- caseless ammunition, etc.?
5. etc.

The list can be a lot longer, and part of our discussion may illuminate the things that really count!

[RedFalconBill]

HITS is nothing more than:

(Bullet Sectional Density x Bullet Weight (in grains) x Impact Velocity)/100

How does this measure lethality?

[JASmith]

Actually, the HITS score is more precisely described as a measure of lethality potential for bullets of similar construction but different sizes. The product of velocity and sectional density gives a measure of penetration depth. The product of this and the bullet weight is a measure of or material available for fragments.

The metric allows comparisons between calibers and appears to give results reported be be consistent with a fair bit of experience.

Keep in mind that a poor impact location trumps the most lethal bullet and that the events are random, so precise measurements are problematic.

[RedFalconBill]

Actually, no it is not a precise measure of lethality. The key word in your third sentence is "appears". Bullet construction is equally important, if not more so. It is much like the OGW equation in Lyman's Reloading Manual in that it claims to be something it is not.

Read the BTB work done years ago by request of the USMC, which resulted in the Mk317 (7.62x51) and Mk318 (5.56x45).

If Big Army real wanted to increase the lethality of its current crop of carbines and rifles, they would adopt a better bullet than the M-855/SS-109, but all Big Army wants is the phased plasma rifle in the 40 watt range.

Just how would you get more 'power' (using the HITS formula) than the 7.62x51 at 100 Meters and keep the carbine under 3kg (empty, with no accouterments) and have enough firepower within the 10kg load limit that Big Army wants and not overpower the Soldiers?

[JASmith]

Ref Post #4: "Actually, no it is not a precise measure of lethality." -- That is precisely correct in the sense that impact location makes a huge difference in how the target responds. Further, the metric assumes bullets of similar construction.

As far as the "100 meters" -- my apologies, the reference is for 1100 meters (the post has been corrected). At this range, the M80 has slowed to about 1000 ft/sec. A 123 gr 6.5 projectile matches the HITS score at about 1055 ft/sec. Getting this velocity at 1100 meters with a BC of about .520 requires a muzzle velocity of approx 2550 ft/sec. This is a fairly tolerable load.

[RedFalconBill]

Considering that at ranges beyond 300m and especially past 400m the infantry squad is better off using the M-240, the added power many of the rounds touted as replacements will be wasted.

The two rounds that would be the easiest to upgrade from the 5.56x45 would be the 6x45 and the wildcat .25 Bailey. While both would be a quick upgrade, the upgrade they provide is not worth the cost.

FWIW, I think that the parameters laid down for the 6.8 SPC are about right.

1) At 100m, the SPC round, when fired out of a 16" barrel carbine, had to have at least 200fps more velocity than the 7.62x39, when fired out of an AK/AKM/AK-103.

2) When fired out of a Mk12 style carbine, the SPC round had to have more KE from 0m to 500m than the Mk262 round, when fired out of a Mk12.

Not very aerodynamic though.

[JASmith]

Can you tell me more about the .25 Bailey?

Also, the quest is for a cartridge that would fulfill the GPMG role, so it would be in either the M-240 or whatever weapon replaces the M-240.

So, the resulting cartridge would replace both the 5.56 and the 7.62 NATO rounds in just about everything but the aviation applications. I will note, however, that the folks pushing this haven't discussed the vehicular, aviation, or Gatling gun roles the 7.62 NATO is also used for. I think the discussion will ultimately have to enter this area as well, and might drive a conclusion that what we currently have is about as good as it gets.

If the debate did not include the GPMG mission but covered only the assault rifle through battle rifle, including designated marksman role, then I think a strong argument exists for a 90 gr .224" bullet in a cartridge based on the .22 PPC. Problem is that the GPMG is normally part of the platoon, and the goal is to keep the platoon lethality at least as high as it is now while either reducing weight carried or increasing number of rounds within the current weight carried. That seems to be driving the discussion to calibers larger than .224" or 5.56mm.

So, it comes down to how we define equivalence...

[LR1955]

Joe:

Here is a problem with the conditions. You are using data based off of a 123 Lapua Scenar match grade bullet in comparison with M-80. Two different animals with huge differences in quality and particularly cost. This is the major flaw in the Grendel argument. I think Lapua quotes a G-1 BC (yes, I know it isn't the right BC to use but it suffices) of somewhere around .54 I think. And that is real questionable. Certainly, such a bullet shot at 2650 will match M-80. Reduce it to a rational ball round and then things change real fast.

I believe a ball round of 6.5 G that can give any sort of reasonable velocity given current powder technology will probably be in the 110 grain range and its BC will be the same as M-80 most likely. It may be higher but I bet it won't be high enough to show statistical significance. And I doubt you will get that 110 grain bullet to leave a barrel as fast as a round of M-80 given the same barrel length. Even if it does, the HITS formula changes due to the lighter bullet.

So, the debate in terms of effective range needs to reflect the reality of a Grendel "ball" cartridge fired at what ever velocity one can get from the specific barrel length with the constant being about 30 grains of powder.

So far, I tend to agree with RFB and my view has always been that the Army can design a bullet for the 5.56 that is more lethal on humans if the Army wants to. And it is doing so and the bullet will probably give a higher degree of lethality than the issued 855. I bet the old 193 has a higher lethality potential than the 855.

A question though. Why the 1100 meter lethality range? I mean, what is the rationale for that distance?

LR55

[RedFalconBill]

Can you tell me more about the .25 Bailey?

The .25 Bailey is the .223 Remington with the shoulder pushed back 5mm, necked up to accept 0.257" bullets and the case 1.575" long.

This is done for a few reasons.

1) To keep existing case taper
2) To allow for current M27 disintegrating links
3) To have the 0.257" bullet diameter at the same point as the 0.253" 5.56x45 case neck in order to use existing 20 and 30 round magazines w/o the stacking issues other rounds have

With a 16" barrel, the Bailey sends the 100gr Sierra GK bullet out at 2,520-2,560 fps. With the 100gr Sierra MK, about 30-50 fps slower.

Also, the quest is for a cartridge that would fulfill the GPMG role, so it would be in either the M-240 or whatever weapon replaces the M-240.

I would include a third GPMG in the infantry platoon and look to getting either the M-240L or MK-48 in their hands.

If the debate did not include the GPMG mission but covered only the assault rifle through battle rifle, including designated marksman role, then I think a strong argument exists for a 90 gr .224" bullet in a cartridge based on the .22 PPC.

A 90gr match bullet is very long, would require a fast twist and is, IMO, the wrong direction to go for a general purpose Infantry firearm.

[JASmith]

The .25 Bailey is the .223 Remington...

Thanks -- that's an interesting cartridge and might be fun to shoot!

I would include a third GPMG in the infantry platoon and look to getting either the M-240L or MK-48 in their hands.

One of the possible outcomes of the discussions is very much along the lines you suggest: Get the best practicable lethality and range from the 5.56 and increase the numbers of 7.62X51. Problem with the second part is the Tony Williams debate indicates that all those M80 rounds weigh a lot.

A 90gr match bullet is very long, would require a fast twist and is, IMO, the wrong direction to go for a general purpose Infantry firearm.

You may be right, but we need to establish rational alternatives to inform a debate. The analysis suggests that the heavy bullet might work, but not necessarily as a GPMG cartridge substitute.