The 6.5 Grendel As a Unified Military Cartridge

John Hanka
February 22, 2005

Being a military buff, I’m always asking myself questions such as: What’s the best main battle tank? What’s the best jet fighter? What’s the best assault rifle? And then there came the day when I asked myself: What’s the best assault rifle cartridge? After studying the issue for a while and giving it quite a bit of thought, I typed into Google’s search engine: 6.5 PPC. The search results lead me to Arne Brennan’s early website describing his experiments with the 6.5 PPC which, in collaboration with Bill Alexander of Alexander Arms, was to become the 6.5 Grendel.

Subsequently, I created this website and began my online advocacy of the 6.5 Grendel as a general-purpose military cartridge for assault rifles, man-portable machine guns, and designated marksman rifles for ranges from zero to 1,000 yards and as a replacement for both the 5.56 NATO and 7.62 NATO. In response to a challenge on another forum, I had set down my thinking on the issue in a somewhat orderly fashion, and have reproduced those basic arguments here for your consideration.

First of all, what do I actually propose? I contend the 6.5 Grendel should replace both 5.56 and 7.62. I propose a three-cartridge small arms system: (1) A pistol cartridge for pistols and submachine guns. (2) The 6.5 Grendel for assault rifles, man-portable machine guns (includes what we now call LMGs and MMGs), and designated marksman rifles. (3) Vehicle mounted and heavy anti-material would be handled by .50 BMG. Dedicated snipers with very specific needs can use any cartridge/weapon combo they’re willing to lug into the field. Now, if this proposal seems radical, consider that that is how we fought World War II. We had the .45 ACP for pistols and SMGs, the .30-06 for rifles and machine guns, and the .50 BMG. Now, of course, we had the .30 Carbine, but that was intended to be a pistol replacement, and not a general-purpose rifle cartridge. I’m proposing the 6.5 Grendel as a new general-purpose rifle cartridge.

I base my advocacy of the 6.5 Grendel roughly on the military studies coming out of World War II that the .30-06 was too heavy and the ideal small-arms cartridge should be something like the British .280. My thinking is based on acceptance of the general consensus of the postwar studies by the major participants, including the thinking that gave the Russians their 7.62x39 M1943. I accept the assumption that 99% of infantry firefights take place within 500 meters, and probably 85% take place within 300 meters. I still want a realistic long-range capability, however, for DMRs and the machine guns. And I don’t think the need for true long-range capability is in dispute, even given the above assumptions, because, for whatever reasons, the current U.S. military requirement includes 800-meter effectiveness, or more.

My proposal rests on the assumption that the current two-cartridge system is more by accident than by any master plan. It may actually have turned out well, and we’re getting along nicely with it, but it’s not absolutely dictated by any combat requirements that a military must have a two-cartridge shoulder arms system! So I consider it up for reasonable debate.

My proposal assumes that a one-cartridge system will have big-picture pay-offs in the realms of logistics and budgets. No more designing two sets of every weapon: a SCAR-L and a SCAR-H, a Mk 11 and a Mk12, an M249 and an M240, etc. No more worrying about whether you brought enough 7.62; everybody uses one cartridge, and this is helpful in a pinch. At this point, you might argue that the Russians, even in the heyday of their 7.62x39, maintained their 7.62x54 for the medium machine gun. I will grant this is a good point. However, the 7.62x39 never had ballistics that could equal those of their full-power cartridge; the 6.5 Grendel changes all that, shooting as flat, or flatter, than both 7.62 NATO M80 ball and M118LR!

It rests on the assumption that if 5.56 terminal ballistics are “good enough,” then 6.5G terminals also are. Moreover, any increase in terminal effect of the 6.5G over 5.56 is, as they say, “gravy.” The 6.5G hits with roughly twice the lead mass of 5.56, so you have the potential for twice the mass of fragments and, if maximum fragmentation is coincident with maximum temporary cavity, you’re going to have very convincing terminal effects. And the short answer to concerns about overpenetration before yaw is that, firstly, there’s more than one theory of where, exactly, a bullet should begin yaw in gelatin and, secondly, a new bullet can be engineered to specific requirements, if a given off-the-shelf bullet doesn’t happen to be ideal. This is what Hornady did with their 6.8 115gr OTM, for example.

It assumes that we don’t call upon 7.62 NATO weapons to improve soft-target terminal ballistics, we call upon them for increased range and penetration of intermediate barriers or light armor. I’m assuming that if 5.56 terminal effects in soft targets are “good enough,” then 7.62 terminals would be “overkill.” Thus, for 6.5G to replace 7.62, it doesn’t need to equal the soft-target terminal effects of 7.62, it needs to equal (or exceed!) the range and penetration of 7.62. If we truly felt 7.62 terminal effects were absolutely NEEDED across the board, we wouldn’t allow line units to be equipped with only 5.56! Nobody says, “Hey! My 5.56 isn’t lethal enough, bring in the 7.62s!” They say, “Hey! My 5.56 doesn’t have enough range or penetration, bring in the 7.62s.” You don't need a 7.62 MMG just to “keep their heads down”; you’ve got M249s for that. So if 6.5G can equal the range and penetration of 7.62, it’s a valid replacement, even if I’m replacing a 147gr bullet with a 123gr.

I am intrigued by the fact that we could give every troop in the line the range and penetration of 7.62 M80 in a compact cartridge that fits in the size envelope of 5.56 M855! Such an increase in firepower would definitely teach the enemy the difference between cover and concealment. And where the amount of effective cover is reduced on the battlefield, enemy casualties must increase. And where the enemy has been chased from cover that formerly stopped 5.56 and has been “herded” into available cover that can stop 6.5 Grendel with it’s ability to penetrate like 7.62 M80, a well-placed smart munition should be cost-effective.

All of cartridge design is a study in compromise. Alas, though there’s an increase in capability with an intermediate cartridge, there’s also a corresponding increase in weight; a basic load of 210 rounds of 6.5 Grendel ammo brings a weight increase of about 2.4 pounds over 5.56. If you want to carry the same weight in 6.5G as you currently have in 5.56, you reduce the basic load from 210 rounds to 147. Please realize that there’s no “magical” number of rounds in the basic load, these things are up for debate. We won World War II, for example, with a basic load of 80 rounds of .30-06!

How to deal with the weight issue? One of my answers is that it’s already an unspoken doctrine that you “double-tap” with 5.56. If one round of M855 5.56 weighs 186 grains, and one of 6.5G 123gr weighs 265 grains, then using two 5.56s for one 6.5G actually uses 140% more ammo weight! So I would argue that the increase in effectiveness of the individual round offsets some of the weight increase. Having said that, experienced combat troops take as much ammo as they can carry, anyway, and a former Marine who fought in the early Hill Country battles in Vietnam swears to me that being able to carry a lot of rounds of 5.56 kept him and his buddies from being overrun. So a realistic basic load is a serious issue.

Having acknowledged that reduced ammo weight is a worthy goal, we must realize that this, too, is an arbitrary figure, open to debate. For example, if you carry an ammo weight-saving initiative to the extreme, we’d all be armed with .22 LR! Obviously, a compromise needs to be made between cartridge weight and projectile effectiveness. The debate between the weight of 5.56 and 6.5G simply rests in where you decide to draw the line. I find the “optimum compromise” in an intermediate position between 5.56 and 7.62, and I think the combination of post-WW2 studies and recent, real-world experience with 5.56 deficiencies supports this. So I suggest we find ways to shave 2.4 pounds in other gear to allow an intermediate-cartridge basic load that brings with it no weight penalty.

But where a shorter-range intermediate cartridge would simply add weight to the overall burden but only give limited additional capabilities, it’s different with the 6.5G. Because the longer-range 6.5G also replaces the range and penetration of 7.62 NATO M80, it allows you to offset some of the earlier weight increase by greatly decreasing the weight for an M240 machine gun team, as I’ve detailed elsewhere. For the same weight of 2,000 rounds of 7.62, you can carry 2,924 rounds of 6.5G, or you can have 2,000 of 6.5G and save 35 lbs on ammo alone (not including a lighter MG weight).

The two things that would make my arguments invalid would be if the 6.5 Grendel had worse terminal performance than 5.56 and worse range and penetration than 7.62. These things need to be rigorously and scientifically tested; some have already taken place, and more are to come.

What seems clear to me at this point is that there is no technical reason the 6.5 Grendel couldn’t serve our military as a general-purpose replacement for both 5.56 and 7.62; it’s a matter of political will. I would like to see some innovative soul study the logistical and financial efficiencies we’d gain from having only one set of general-purpose weapons and one cartridge, instead of our current system cobbled together that dictates a 5.56 version and also a 7.62 version of basically the same weapon.