An Analysis of the Soldier’s Load with 6.5mm Cased Telescoped Ammunition (Part 2)

One thing that seems apparent from the ARDEC presentation on the CTSAS program is the excessive capability and weight of the 6.5mm CT ammunition, as well as its use of lead-cored projectiles as opposed to more modern (and less dense) EPR-type projectiles. Further, the 6.5mm configuration explicitly uses the same case as the 7.62mm CT round, to allow for shorter development times. These facts together indicate that the 6.5mm CT round demonstrated in the ARDEC presentation is not well optimized for minimum weight. For this post, we’ll create an estimate of a new, lighter round that still should be powerful enough to replace both 5.56mm and 7.62mm as a universal caliber. As mentioned in the previous post, we’ll call it the “LW 6.5mm CT” to differentiate it from ARDEC’s 6.5mm CT round.

Fortunately for me, I have already modeled a 6.5mm* low-drag EPR-type projectile, which has made cameos in the title images of a few of my previous articles:


*Quick fun fact for those reading this who believe I am a 5.56mm fanboy: .264″/6.5mm is actually the default caliber I use for projectile design in SolidWorks, and the products then get scaled up and down to other calibers if I need them.

This projectile weighs 7 grams (108 grains) and has a calculated i7 Form Factor of 0.86 giving it a G7 BC of 0.257, although for the purposes of this article we will use the more modest 0.90 i7 FF and 0.246 G7 BC to account for difference between theoretical and actual values. It has an overall length of just over 34mm even (1.339 in), and is based on the shape of the Berger 130gr AR Hybrid 6.5mm bullet, but with construction patterned after the M855A1 and M80A1 EPRs developed by the Army.

To determine the weight of the ammunition that will use this bullet, we will need to determine what capability it will need. The 6.5mm CT ammunition in the ARDEC presentation matches the energy produced by 7.62mm M80 Ball at a kilometer out to 1,200m, which seems excessive. At the very least, matching 7.62 NATO at a kilometer, instead, would seem to meet the needs of a single-caliber system, but due to the smaller diameter of the 6.5mm projectile, less energy is likely needed to achieve the same penetration. While one could do an exhaustive study to determine the ideal muzzle velocity and energy, I will instead just eyeball it. 6mm SAW was a caliber designed in the 1970s as the “ideal” squad automatic weapon caliber, and it launched a 105 grain bullet with a similar ballistic coefficient at a muzzle velocity of about 2,550 ft/s. We’ll use this muzzle velocity, too, which gives 2,115 Joules of muzzle energy, and – using JBM’s excellent ballistics calculator – 344 J of energy at 1,000 meters, and more specific energy (energy divided by bullet frontal area) than 7.62mm M80 Ball – and coincidentally a pleasantly flat trajectory, as well.

To estimate the weight of this round, we can create a modifier to determine the mass of a plastic telescoped case based on the figures given to us in the ARDEC presentation. We know, for example, that the 5.56mm CT round weighs 127 grains, or 8.23 grams, whereas a standard round of M855 weighs 12 grams. Subtracting the components that remain the same between the two, we get:

12 grams – 4 gram bullet – 0.25 gram primer – 1.72 gram propellant = 6.03 gram case weight

8.23 grams – 4 gram bullet – 0.25 gram primer* – 1.72 gram propellant* = 2.26 gram case weight

*We actually do not know the weight of primer and propellant for 5.56mm CT, but the error shouldn’t be significant for the purposes of this article.

That means case weight was reduced by 62.5%, so we can multiply the case weight of an existing round by 0.375 to get the approximate weight of the PCT case. Let’s check this process using 7.62 NATO and 7.62 CT:

23.1 grams – 8.43 gram bullet – 0.35 gram primer – 2.98 gram propellant = 11.34 gram case weight

11.34 grams * 0.375 = 4.25 gram CT case weight

4.25 grams + 8.43 grams + 0.35 grams + 2.98 grams = 16.01 grams CT cartridge weight

Actual weight of 7.62mm CT is 15.6 grams, so this process does produce a fairly accurate result. Now, we need to select a case to start with, ideally one with similar muzzle energy and the same caliber. A suitable candidate exists in the form of 6.5 Grendel:

17.8 grams – 8 gram bullet – 0.25 gram primer – 1.90 gram propellant = 7.65 gram case weight

7.65 grams * 0.375 = 2.87 gram CT case weight

Now, we’ll be using a different weight projectile for the example (7 grams instead of 8), but that’s a simple matter of plug-and-play:

2.87 grams + 7 gram bullet + 0.25 grams + 1.90 grams = 12.02 grams CT cartridge weight

I’ll go ahead and round that to an even 12 grams. We can also estimate the weight of the LW 6.5mm CT belt link by averaging the weight of the 7.62mm and 5.56mm CT belt links:

0.84 gram 5.56mm CT belt link + 1.46 7.62mm CT belt link = 2.30 grams

2.30 grams / 2 = 1.15 grams

Now, we just need to find the weight of magazines. To do that, we need some idea of the size of the LW 6.5mm CT case, but that’s straightforward enough. Let’s take the approximate case weight for 7.62mm CT and divide the weight of the LW 6.5mm CT case by it:

2.87 grams / (15.6 grams – 8.43 grams – 0.35 grams – 2.98 grams) = 2.87 / 3.84 = 0.747

This indicates how much smaller a 20 round LW 6.5mm CT magazine would be than a 20 round 7.62mm or 6.5mm CT magazine. We got a value of 150 grams before for the 20 round 6.5mm CT magazine, and while I don’t like to multiply an estimate by an estimate, it’ll have to do:

0.747 * 150 = 112 grams

Now, I would like to use 30 round magazines for this, and we know that a 30 round PMag weighs about 47% more than a 20 round PMag, so we can estimate a 30 round magazine by:

1.47 * 112 grams = 165 grams

So then our values are:

Weight of 1 round of LW 6.5mm CT: 185 grains / 12.0 grams
Weight of 1 belt link for LW 6.5mm CT: 17.7 grains / 1.15 grams
Weight of 1 30-round LW 6.5mm CT magazine: 2,546 grains / 165 grams

Now we can simply plug them in:


Infantry Squad:

Squad Leader: 210 rounds LW 6.5mm CT in 7 magazines totaling 3.675 kg
Team Leader: 210 rounds LW 6.5mm CT in 7 magazines, 200 rounds linked LW 6.5mm CT totaling 6.305 kg (x2)
Automatic Rifleman: 800 rounds linked LW 6.5mm CT totaling 10.520 kg (x2)
Grenadier: 210 rounds LW 6.5mm CT in 7 magazines, 200 rounds linked LW 6.5mm CT totaling 6.305 kg (x2)
Rifleman: 210 rounds LW 6.5mm CT in 7 magazines, 200 rounds linked LW 6.5mm CT totaling 6.305 kg (x2)

Weight of ammunition of infantry squad: 62.545 kg (x3)


Weapons Squad:

Squad Leader: 210 rounds LW 6.5mm CT in 7 magazines totaling 3.675 kg
Machine Gunner: 300 rounds linked LW 6.5mm CT, totaling 3.945 kg (x2)
Assistant Gunners: 210 rounds LW 6.5mm CT in 7 magazines, 400 rounds linked LW 6.5mm CT totaling 8.935 kg (x2)
Ammunition Bearer: 210 rounds LW 6.5mm CT in 7 magazines, 300 rounds linked LW 6.5mm CT totaling 7.620 kg (x2)

Weight of ammunition of weapons squad: 44.675 kg


Platoon HQ:

Platoon Leader: 210 rounds LW 6.5mm CT in 7 magazines totaling 3.675 kg
Platoon Sergeant: 210 rounds LW 6.5mm CT in 7 magazines totaling 3.675 kg
Radio Operator: 210 rounds LW 6.5mm CT in 7 magazines totaling 3.675 kg
Combat Medic: 210 rounds LW 6.5mm CT in 7 magazines totaling 3.675 kg

Weight of ammunition of platoon headquarters: 14.700 kg


So with our LW 6.5mm CT example cartridge, the infantry platoon’s load is reduced by 12% to 247.010 kilograms, and the weight of the weapons squad is absolutely slashed down to 44.675 kilograms from 80.911 kilos, a savings of 45%! Versus ARDEC’s 6.5mm CT, moving to a less ambitious universal caliber reduces weight in the infantry platoon by 23%, given the same number of rounds (I’m including those 15 spare magazines from last time), a considerable improvement.

Lighter ammunition paradigms are yet possible, though. Let’s see what happens if we retain the dual-caliber system, and use 5.56mm CT alongside the CTSAS 6.5mm CT, replacing one-for-one the two current conventional brass-cased calibers. Remember the values for these rounds are:

Weight of 1 round of 6.5mm CT: 237 grains / 15.4 grams
Weight of 1 belt link for 7.62mm/6.5mm CT: 22.5 grains / 1.46 grams
Weight of 1 20-round 6.5mm CT magazine: 2,320 grains / 150 grams

Weight of 1 round of 5.56mm CT: 127 grains / 8.2 grams
Weight of 1 belt link for 5.56mm CT: 13 grains / 0.84 grams*

We’re missing the weight of a 30 round magazine for 5.56mm CT, but a value of 110 grams seems reasonable based on the weight of 30 round polymer magazines for brass-cased 5.56mm. I also simplified the ammunition bearer’s loadout by having him only carry 6.5mm ammunition, 140 rounds of it in magazines, presumably for a lightweight 6.5mm Designated Marksman’s Rifle.


Infantry Squad:

Squad Leader: 210 rounds 5.56mm CT in 7 magazines totaling 2.492 kg
Team Leader: 210 rounds 5.56mm CT in 7 magazines, 200 rounds linked 5.56mm CT totaling 4.300 kg (x2)
Automatic Rifleman: 800 rounds linked 5.56mm CT totaling 7.232 kg (x2)
Grenadier: 210 rounds 5.56mm CT in 7 magazines, 200 rounds linked 5.56mm CT totaling 4.300 kg (x2)
Rifleman: 210 rounds 5.56mm CT in 7 magazines, 200 rounds linked 5.56mm CT totaling 4.300 kg (x2)

Weight of ammunition of infantry squad: 42.756 kg (x3)


Weapons Squad:

Squad Leader: 210 rounds 5.56mm CT in 7 magazines totaling 2.492 kg
Machine Gunner: 300 rounds linked 6.5mm CT, totaling 5.058 kg (x2)
Assistant Gunners: 210 rounds 5.56mm CT in 7 magazines, 400 rounds linked 6.5mm CT totaling 9.236 kg (x2)
Ammunition Bearer: 140 rounds 6.5mm CT in 7 magazines, 300 rounds linked 6.5mm CT totaling 8.264 kg (x2)

Weight of ammunition of weapons squad: 47.608 kg


Platoon HQ:

Platoon Leader: 210 rounds 5.56mm CT in 7 magazines totaling 2.492 kg
Platoon Sergeant: 210 rounds 5.56mm CT in 7 magazines totaling 2.492 kg
Radio Operator: 210 rounds 5.56mm CT in 7 magazines totaling 2.492 kg
Combat Medic: 210 rounds 5.56mm CT in 7 magazines totaling 2.492 kg

Weight of ammunition of platoon headquarters: 9.968 kg


This arrangement is the lightest yet, with a total weight of 185.844 kilograms for the platoon, a savings of almost 100 kg, or 34%, versus the current brass-cased dual caliber system, and a savings of 42% – almost 135 kilograms! – versus a single-caliber system using the 6.5mm CT proposed by ARDEC. That’s an average weight reduction of over 3.5 kilograms (almost 8 pounds) per person, a very substantial difference.

It doesn’t, however, address the concerns some have about the infantry squad’s ability to project fire to longer ranges. One possible (and very light) solution to that would be to issue a unified belt-fed caliber for a new weapon that would replace both the 7.62mm M240 machine gun and 5.56mm M249 automatic rifle, while issuing carbines in a lighter, smaller caliber. That might look like this:


Infantry Squad:

Squad Leader: 210 rounds 5.56mm CT in 7 magazines totaling 2.492 kg
Team Leader: 210 rounds 5.56mm CT in 7 magazines, 200 rounds linked LW 6.5mm CT totaling 5.122 kg (x2)
Automatic Rifleman: 800 rounds linked LW 6.5mm CT totaling 10.520 kg (x2)
Grenadier: 210 rounds 5.56mm CT in 7 magazines, 200 rounds linked LW 6.5mm CT totaling 5.122 kg (x2)
Rifleman: 210 rounds 5.56mm CT in 7 magazines, 200 rounds linked LW 6.5mm CT totaling 5.122 kg (x2)

Weight of ammunition of infantry squad: 54.264 kg (x3)


Weapons Squad:

Squad Leader: 210 rounds 5.56mm CT in 7 magazines totaling 2.492 kg
Machine Gunner: 300 rounds linked LW 6.5mm CT, totaling 3.945 kg (x2)
Assistant Gunners: 210 rounds 5.56mm CT in 7 magazines, 400 rounds linked LW 6.5mm CT totaling 7.752 kg (x2)
Ammunition Bearer: 210 rounds LW 6.5mm CT in 7 magazines, 300 rounds linked LW 6.5mm CT totaling 7.620 kg (x2)

Weight of ammunition of weapons squad: 41.126 kg


Platoon HQ:

Platoon Leader: 210 rounds 5.56mm CT in 7 magazines totaling 2.492 kg
Platoon Sergeant: 210 rounds 5.56mm CT in 7 magazines totaling 2.492 kg
Radio Operator: 210 rounds 5.56mm CT in 7 magazines totaling 2.492 kg
Combat Medic: 210 rounds 5.56mm CT in 7 magazines totaling 2.492 kg

Weight of ammunition of platoon headquarters: 9.968 kg


That gives a weight of ammunition carried by the platoon of 213.886 kilograms, which is less of a reduction in weight than the previous example, though it still eliminates over 67 kilograms (24%) versus the current system. Complementing that, it would not only reduce the number of weapons in service (as the GPMG and SAW would be combined into one), but would also give the automatic riflemen organic to the infantry squads capability and range very close to current GPMGs but with a far greater ammunition load, while still retaining the good handling and recoil characteristics of current 5.56mm carbines and reducing weight beyond what is possible with a one caliber system.

To conclude, that’s what the weight breakdowns of different future ammunition paradigms look like for the infantry platoon. It should be noted that I am backing no one concept, though I have insisted for some time now that the benefits of the two-caliber system should not be ignored moving forward. These examples help make clear why, although they make very clear the benefits of one-caliber systems, as well.

Mostly, though, they illustrate what a promising technology polymer cased telescoped ammunition really is. In all cases, the weight carried by the most burdened unit – the weapons squad – was significantly reduced, and in particular all examples dramatically reduced the weight carried by the ammunition bearer in the squad, who currently carries the most weight in ammunition of any member of the platoon.

Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. In addition to contributing to The Firearm Blog, he runs 196,800 Revolutions Per Minute, a blog devoted to modern small arms design and theory. He is also the author of the original web serial Heartblood, which is being updated and edited regularly. He can be reached via email at


  • Tassiebush

    remember that notion that efficiency would lead to more leisure time? i suspect this would result in either more ammo or equipment being added rather than soldiers spared the load. still worthwhile and a winning edge though.

    • kregano

      That literally happens with EVERY military thing. We develop new, lighter ammo – we stick more on the infantryman, so he now has to carry the same weight. We develop new, smaller equipment – we shove more into our ships and submarines so there’s no extra room for the crew. And so on and so forth.

      • randomswede

        In the post cold-war era it seems to be even worse as no ammo was “taken away” to make room för NVGs or bodyarmour, perhaps if the CTSAS is successful in outperforming the current platforms in every way and shows further potential the load would lighten for a while atleast.

        • Major Tom

          Nope. Say these programs are successful and it saves a soldier 5 lbs of load. Some buffoon of an officer or monkey-who-don’t-give-a-s*** senior NCO is going to make you carry an extra medkit or some useless electronic doohickey that you’ll never use. And enough of it to offset the losses in weight.

          And considering at least half the gear you’re issued on deployment is rarely if ever used…

          • randomswede

            Hence the “perhaps”.

          • AmmoMFG (Drew)

            “oh, you’re not at 120lbs? Here carry these mortar rounds”

            I remember reading somewhere the ideal “load” is about 1/3 of body weight max. I’ve seen some of these poor SOBs carrying loads up to 2/3 of body weight. For a highly mechanized force, this is fine, because all that gear stays in the truck, but there’s a serious need to just have soldiers carry less crap, regardless of how light it is.

          • CommonSense23

            1/3 is the weight you can carry for sustained operations without injury.

          • Kivaari

            Or so it is “hoped”.

          • And 50% is the max you can carry without being so worn out you need hours to recover to full capacity, In addition to causing *permanent* injuries when routinely done for extended periods.

          • CommonSense23

            Where are you getting those stats from, never heard them before.

          • raz-0

            Or more batteries. It’s like ammo for your electronics.

    • Austin

      Level IV plates for everyone?

    • The_Champ

      I’ve brought this up before, but I think it’s worth saying again; has anyone explored the idea that other common equipment that soldiers carry can be lightened up as much or more than the weapons system, and at much less cost?

      What I mean is, if we are trying to shave 5-10 pounds off our soldiers, why not do it with ruck sacks, sleeping bags, jackets, water bottles, electronics, batteries, etc, and keep the conventional weapons that work. Surely this could be done in a cheaper fashion than a whole new weapon and ammo system.
      I’m approaching this from a cost perspective of course. If the cost is no consideration, then do both I guess. Lighter weapons AND lighter gear.

      • The load on the soldier is such that ALL equipment needs to be subject to weight reduction, yes.

      • politicsbyothermeans

        PEO Soldier puts lots of effort into lightening up the load. Even so, observations from JRTC and AARs from redeploying units indicate that the average weight of combat loads just keeps going up. Quite a bit of effort has gone into designing relatively lightweight universal batteries and things live NVGs are way lighter now than when I joined in 19mumblegrumble. PVS-5s weighed something like 850g and the PVS-14 weighs less than half of that with the old 5s using 2 AA batteries (after a conversion) while the 14 uses 1. Modern MICH helmets are definitely lighter, especially compared with steel helmets.

        Until we either have assisted powered exoskeletons or land based drones carrying most of the platoon’s gear, I’m sure that there will be lots of effort to lighten the overall load.

        • But there’s a reason why light infantry used to avoid armor like it was a biohazard… however much protection it provides, the prevailing thought was that it slowed us down and wore us out so much, we not only *couldn’t* do our actual job (extended dismounted operations), but would actually *increase* casualties – not just mission kills on the body from the weight, but actual kills from having reduced situational awareness from fatigue and from being too heavy to manuever.

          • politicsbyothermeans

            Brother, I am with you 100%. I remember the NTC/JRTC rotations prior to 9/11 when we had to be “fit to fight” and wear flak vests. It was miserable. Little did I know that that Interceptor was right around the corner and that the good old days of occasionally wearing flak vests would be sorely missed.

            It really wasn’t so bad in Iraq as we usually rode to work, dismounted, did our thing and then mounted up for a ride back to the COP/FOB. Trashcanistan was a whole other thing. I cannot adequately express the rage I felt when a flat-bellied steely-eyed killer told me that he wasn’t sure he could go on because he was smoked after humping 12+km and 2000+feet. We’re not talking about marginal guys either. These are guys that were on the extended scale when we were at home station. All of the ballistic protection in the world didn’t do us a damned bit of good when I had to leave some of my better Soldiers behind watching rucksacks while the rest of us kicked in doors.

          • But the days of doing a night recon and infiltration with soft caps, no webbing, and one mag per pocket are as dead as a 20″ rifle with a fixed carrying handle. ?

          • politicsbyothermeans

            Preach. I decided to ditch the Army the day I had to get an O6 signature to conduct a linear ambush in an AO where the good Colonel couldn’t find without 24 hours, a DAGR and a full staff.

            More realistically, if stretches human endurance to expect kids to hump 90+ lbs to the objective and then kick the crap out of someone who is either at home or isn’t carrying a lot more than a few belts of 7.62 and a blanket.

          • M.S.1

            “the days of doing a night recon and infiltration with soft caps, no webbing, and one mag per pocket are … dead”

            But the REAL question is: should they be?

      • iksnilol

        I skeletonize and shorten the handles on my toothbrushes.

        Does that help?

      • Greg Kelemen

        What about the other side of the issue, a new super-efficient load
        bearing system based on something like the tumpline packs of yesteryear.

        Alpinist packs are for light duties, carrying the bare necessities for
        an ascent.

    • Rock or Something

      Bring on the load bearing mules with MK19s!

      • Ron

        That is a Mk47 Striker AGL

        • Rock or Something

          Even better.

      • Tassiebush


  • randomswede

    A further hypothetical alternative just struck me:
    Essentially the LW 6.5 CT suggested here loaded into a case with the same length and diameter as the “fullsize” 6.5 CT, not as light as it could be and the same volume but fires equally well from any weapon system.

    A largely useless concept unless the lighter round isn’t notably lighter and/or cheaper.

    • Jay

      The LW 6.5 CT in today’s article is optimized for the caliber.

      • George

        Yes, it was, but Randomswede has a point.

        In conventional rounds the case is too heavy to do that. CTW reduces “dead case” weight penalty significantly. There are three costs that matter to doing it:

        1. Heavier case (marginally for CTW)
        2. Heavier magazines (volumetric based wt) but not links (too badly).
        3. Longer / wider receiver and chamber and system effects secondary to that.

        Having that flex could be very useful… But needs numbers.

        • I don’t see the point. Honestly, belted ammo and loose rounds in magazines might as well be different calibers altogether, militarily speaking.

          Who here has had to routinely link or delink ammo belts to take advantage of ammo commonality between their *issue* MG and their *issue* rifle, *as a soldier*.

          Only times I’ve delinked ammo on duty for use in a rifle was a handful of times I was scrounging some tracers for my “squad leader” 20 rounder of straight trace I used on live fires to direct fire.

          Admittedly, I’ve linked or delinked thousands of rounds… as a civilian shooter using milsurp ammo or feeding a WWII MG. But while cashing Uncle Sam’s checks? Not so much.

  • DW

    My .02:
    If they truly want a one caliber system, they need to scale back the 6.5. No reason to have glorified M14/AR10 for every single infantryman who used the M4/M16

    • Austin

      I believe for at least the immediate future the plan for this was to replace LMGs, they just have the carbine as an additional option.

      • Jay

        If they decide yo adopt the 6.5mm round they came out with, there’s little chance they’ll replace the 5.56mm carbines.

      • MPWS

        That may be driven by other factors too such as relatively poor report in subjective evaluation by users. M249 is heavy and relatively inaccurate with reach not better than carbine. I believe that was reason Marines have purged it out. LW 6.5CT and M855 is a viable outcome.

      • What is your source on this?

        • Austin

          Its the only role where this legitimately makes any sense, for everything else aluminum case could lighten the load and drop into the suply chain seamlessly. A 9lb gun only makes sense if it’s for a DMR(which would weigh about the same with an optic as this does naked) or a LMG. The LMG is also the only one that has two dominant calibers(the Army has been phasing out the M14 for the M16A4 for a while).

          • So you do not have a source for this information?

  • MPWS

    It is shaping rather well now, but is it all worth it especially given all new individual weapon system which by coincidence appear to be heavier and more complex? You’ve got to strip a round, ram it into chamber, transfer chamber (in straight or rotary motion) into alignment with barrel and fire which is all done in current systems in one single sweep. It comes therefore to cardinal question: is there an overall benefit?

    As one of those who does not dwell in plain critical mode, I ought be able to suggest a ‘creative’ alternative. Based on what I’ve seen the author has done so far, it comes to me as a new 6.5 round in conventional configuration (with perhaps light material case) while keeping with current weapons. That round could be with 2 different bullet weights, something what Chinese have done with their 5.8 x 42 mm shot.
    Big experiment may not be worth of potential trouble. This being said however is not meant that investigation of potential progress is without value; just to contrary. It helps to validate what you already have or may have. It adds measure of confidence; nothing wrong with that.

    • Austin

      If they go with a lighter conventional case I would like to see it be a straight wall case so it could utilize a P90 type in the top out the bottom system

      • Kivaari

        The P90 uses a bottleneck design.

        • iksnilol

          Maybe he meant a case with very little taper?

          Like 5.7 or 5.56.

    • Kivaari

      Using two different bullets in the same caliber is like the 7.62x54mmR round. One 150 grain for rifles and 175 (off the top of my head) for machineguns. Like I mentioned with the Finns during the Winter War ’39-’40. Those millions of captured belted ammo, gave them the notion to re-chamber the rifles to use it. Marking them with a “D” for long range. The heavy load out performed the light load.

    • Tony Williams


      “…a new 6.5 round in conventional configuration (with perhaps light material case) while keeping with current weapons”.

      That would be USAMU’s .264 USA (or the necked-out .277 USA), which is basically a “stretched Grendel” (same case diameter, length increased from 39 to 47mm). The cartridge case weighs 10.3g in brass, 6.0g in MAC LLC’s polymer-with-steel-base. Depending on bullet weight, this gives total weights of around 20g in brass, 15.5-16g in polymer/steel.

      “That round could be with 2 different bullet weights, something what Chinese have done with their 5.8 x 42 mm shot.”

      The Chinese have moved away from that with a new “universal” DBP10 round.

  • therealgreenplease

    Fantastic article. IMO, weight reduction saves lives *and* makes soldiers more effective in combat. For a given capability level (ammo count, effective range, body armor, etc) a lighter soldier will be exposed to fire for less time (crossing streets, getting behind cover quicker), take high ground quicker (fighting in mountainous terrain), and be less fatigued at the end of a patrol (or end of a deployment) which circles the benefits back to my first point.

    This is something the Army really needs to study and pursue, IMO, and I hope they get it right. They need to weigh logistics (how many different rounds are in service) against the effective range of those rounds and the ability of soldiers to actually effectively use weapons at that range and the resulting weight and ammo load.

    • cwolf

      The Army spent $B on body armor. Then families started buying what they thought was better newer armor for their Soldiers. That started Congressional hearings about the mean Army and food fights over advertising promises. So the Army spent more $B fielding “better” armor.

      The rifle & ammo is only part of the load. Every design means trade-offs re lightness and durability. Sure we can make backpacks out of parachute cloth, but durability suffers. Wearing IBA reduces chest wounds, but increases time in combat, increasing arm/leg wounds, etc. Which shifts medical personnel requirements.

      It is an emotional issue. Families want their loved ones to come back in one piece. Our casualty rates are lower due to a variety of things. A Soldier wounded in the morning can be in Germany that night in a hospital.

      I agree. Helmets and IBA are miserable. Somebody design a helmet that doesn’t hold heat in, please. But, they save lives.

      But lighter guys might run faster and not get hit as much. Maybe. The Brit tactical test of tactics showed Russian tactics worked at lower casualty rates. But you have to fight families and Congress.

  • therealgreenplease

    One more thing: it occurred to me that the volume reduction of CT might lead to fewer magazines necessary for a given ammo load. As such you might want to go back and re-run your numbers for such a hypothetical scenario. It’s minor but there would be additional weight savings.

    • Jay

      The reduction in volume comes from shorter overall lenght of the cartridge, but the cases are thicker than their brass counterparts, so i’m not sure you can get more rounds in the mags.

      • therealgreenplease

        Ah, good point 🙁

  • Jay

    This one looks good. Thank you for doing this.
    With this aproach, the weapons squad would also benefit of huge weight savings from much lighter machine guns. I’m not sure how much weight, if any could be shaved off the carbines, if going to your LW 6.5 CT, but i think the reduction in weight of the machine guns would be substantial.

  • forrest1985

    Personally i think a one caliber system will benefit the automatic rifleman massively, especially if the new SAW/MG has an adapter to take magazines as well as belts. Having a common ammo type is certainly advantageous and would surely reduce logistical burdens. Personally i would design a lighter AR platform and DMR to take the “LW 6.5 catridge”. That way all three roles in infantry squad/platoon are covered.Only problem for US would be nato countries still using 5.56 especially when France, UK and a few other countries are already looking at replacing their current issue with 5.56 AR style systems.

    • thmsmgnm

      They tried the magazine thing with the M249 in the early production range….it was not well received…

  • AmmoMFG (Drew)

    For what it’s worth, you’ve done a pretty good job of breaking things down here. However, given the current problems, I highly doubt the military will continue with an EPR type program in the near future given the lawsuit with liberty over the projectile. Even then, the big question I have is whether moving beyond a novel case and gun design while retaining a very conventional bullet design is really what the military should be doing. I know there were developments in the late 1970’s and early 80’s working towards using AP-DS type ammo. Using a steel projectile is always going to be cheaper than anything made of copper, much less copper/bismuth.

    • Kivaari

      That I believe was the “SLAP” and the flachette rounds tested at Picatinny. The rounds so opposed by Fackler’s team. Those “darts” are a bad idea.

      • AmmoMFG (Drew)

        You mean Martin Fackler? I definitely agree that most of the conventional APDS designs (Not SLAP, which was simply a sub-caliber tungsten “bullet”) are probably not ideal for creating wound channels, however this is at least partially due to the very small cross section of previous APDS designs (1.2mm?). Larger bore diameters, allow still larger projectiles, however at the same time as they require more gas to function, they also increase the transferred energy. Further, fin stabilized designs and smooth bore guns allow for much greater muzzle velocities with reduced barrel wear.

        At the moment, most of the LSAT designs use an arrangement similar to a revolver with their reciprocating firing chamber, this greatly affects the weapon’s capability of controlling the high pressure cycle. The only advantage LSAT offers over caseless ammo, is that plastic can be shoved into the space and seal the chamber a bit. As some others have mentioned 5.56LSAT hasn’t shown the velocities desired. Given that 5.56nato has a max operating pressure of 62,500PSI, this is a much more stringent requirement (to contain the pressure) than the normally milder 7.62, which originally was at 50,000PSI (EVPAT now at ~61,000).

        • Kivaari

          Yes, Dr, Fackler. He and I exchanged information. One thing he was particularly against was the foolishness of using flechettes in rifles. His point, and he was correct, it the thing most liked about those little darts is by design they go point forward. Even at very high velocities, even after hitting tissue, the fins orient the projectile point on. So if it hits a person it pokes a small hole. Hit in a non-vital place it’s like an ice pick. Even if they hit vital organs, the holes are often so small that they just don’t do enough damage. He did know his stuff as far as wounds went. Sometimes e focused too much on wounds, and not the combat use for a particular weapon. At a conference he and I participated in, with him being one of the guest speakers, he didn’t get why police or military should use rifles and not shotguns. Prior to that conference a nearby tried to end a kidnapping. The officer fired buckshot at the suspect, and a pellet of 00-buck killed the hostage. Fackler liked shotguns because they delivered a pattern and increased the chances of a hit. Except, we doing the shooting don’t always want a pattern. When I said rifled slugs have 10 inches of drop at 100 yards, a young cop called me a liar. He was one of the “top SWAT cops”, and didn’t know crap. That is a problem too common in jobs where bullets get thrown around. I had a hard time getting Fackler to understand that firing an accurate bullet is better than spraying buckshot all over the place. That same SWAT cop had just recently been in a SWAT situation where one officer was killed because they used a less lethal 40mm sponge round and the suspect fired one round of 7,62x39mm at the team. The early report we got is 5 cops were injured, but all but one was a friendly fire hit. I never found out what “really” happened. So much of what goes wrong is people don’t understand the difference between tactics, ballistics, common sense and reality.
          As for M855 being so high pressure, it is done to get performance at the expense of wear and tear on the carbine. It does need that pressure to get the desired velocity. Personally, I like the M193. Yes, it doesn’t perform like the M855 or the A1 version. In a 20 inch barrel it gives its best velocity, since it WAS engineered to do so. Once cutting barrels to 14.5″ velocity dropped with all the loads. The green-tip loads from what I see are less accurate. Boost the speed, but accuracy goes away, thanks to having that steel insert off center. I’d go for slower, heavier and more accurate like our 77 gr. loads. Ballistics with accuracy is better. Slower, accurate and getting hits is better than having a penetrator. Where do we go from here? Hell, if I know. I’ll keep my M4 with M193. It makes me happy. I’d be happy with some 77 gr, OTM, if someone else is paying for it.

          • iksnilol

            Fackler really didn’t understand why everybody used rifles?

            Wouldn’t that be quite simple to explain with not only wanting to avoid friendly fire, but that you also might on occasion want to hit something that’s more than 50-100 meters away?

          • Kivaari

            It was awkward, since he does know about wounds. He seemed to not get the disadvantages for cops (it was a cop-fire fighter setting) using shotguns v. rifles. He said what do you use hunt birds in a tree, he answered himself by saying a shotgun. I recounted that recent disaster. I said we need rifles in every patrol car and not limited to SWAT. I carried rifles from 1970 until retiring two times.
            Much of that time was with MP5s, just a small rifle. I told my chief why I disliked shotguns, and he listened. Not common in police work. About 2000-1 we shifted to M4s.
            Sometime great brains get too wrapped up in the project. He looked at wounds.
            Fackler knew a great deal about the performance of the common service weapons, since he was in the Army. His work on the 6.5mm Carcano was excellent. He debunked all the conspiracy theories using real science. He justified the research based on the circa 1900 research paper done by the Italian officer. If you can find it, it is in “Wound Ballistics Review, V2 N2 of 1995. We members of the IWBA received them. I regret giving all my copies to a young rookie. I never got them back, with 16 years of waiting.

          • iksnilol

            I literally never heard of anybody shooting birds in a tree with a shotgun. 😛

            I guess, I never was a fan of shotguns at all. I mean, sure, I like the cheap ammo but the shotguns are so handicapped.

            That sucks with losing your research papers. Have you tried tracking him down and b̶r̶e̶a̶k̶i̶n̶g̶ ̶h̶i̶s̶ ̶l̶e̶g̶s̶ asking nicely?

          • Kivaari

            Grouse and squirrels. Grouse are dumb, enough that you can sometime walk up to them just feet away. Lots of hunters in the Pacific Northwest use a .22 pistol or rifle. Kids were known to kill them with slingshots.
            That kid is now deputy chief, and hasn’t learned that he was and remains a pri***.

  • micmac80

    Remember Grenedel , its balistics vere way overhped ,comparing match bullets to much less efficient military bullets.
    One thing that everyone seemed to overlook was lack of velocity.
    5.56 might not the be the biggest or the baddest round out there but one thing it has is flat trajectory that is very important in increasing hit percentage on targets that might no be ranged correctly.For an infantry soldier flater shootign cartridge is way more beneficial than longer ranged slower cartridge. High BC bullets are efficient at retaining velocity at longer range , but succesful long range engagements require accurate ranging which is not present at squad level.

    • Kivaari

      Remember the best 5.56mm combat loads seem to be using Sierra Open Tip Match bullets. Those 77 gr. OTM bullets seem to be working quite well at longer ranges.
      I have not looked at the pressures generated in them. Just that they are accurate, thus better than those bullets that miss.

  • Pedro .Persson

    Who would’ve thunk…

  • roguetechie


    As always you make excellent points and maintain a dispassionate writing of facts for us to draw our own conclusions from. Thank you for having the respect for your reader that you challenge us to think, not tell us WHAT to think.

  • gunsandrockets

    When gunnies looks at guns, the natural tendency is to assume larger weapons should use larger calibers. Hence the notion that belt-fed MG should shoot larger caliber ammunition. But real world combat is demonstrating why that is a problem.

    That’s why the Marines have backed off of the heavy and clumsy M249 and ‘devolved’ back to the M27 IAR for the fire-team automatic weapon. It didn’t make sense to tie the movement of the whole squad to the limited mobility of a support weapon.

    So when speculating about an idealized caliber or mix of calibers for the rifle platoon, how all the elements of the platoon interact should not be overlooked in achieving the best mix of firepower for the whole platoon. And to get even more practical, costs of the weapon systems, and period of transition to any new system should be considered too.

    The biggest bang for the least bucks is to replace all the fire-team M249 LMG with the 5.56mm CT LMG. That provides greatest payoff at the lowest costs of any change to the current Platoon inventory. Fewest number of new weapons, no changes in doctrine or organization, greatest reduction in weight. The 5.56mm CT LMG is like the best of both worlds, the firepower of an M249 and the mobility of the M27.

    If improving longer range firepower is truly so vital to the Platoon, than replacement of M4 5.56mm uppers with 6.5mm grendel caliber upper-receivers could do so at the lowest cost and a modest weight penalty. Preserving a huge base of parts, training, and experience with the M4/M16. Retired uppers from infantry units could be shifted for use in basic training.

    But the simple fact is the entire U.S. military has so much invested in 5.56mm M4/M16 rifles and 7.62mm M240 GPMG, that it is a pipe dream to think they would be replaced at great expense for only minor and mainly theoretical improvements.

    But replacing just the M249? Which have to be replaced anyway because they are mostly worn out? Heck, even the dirt poor Marines are doing that.

    Bring on the 5.56mm CT LMG!

    • therealgreenplease

      It’s not just the U.S. It’s also NATO. From that perspective I wonder if it would be more efficient to start with 6.5 CT for GPMGs, DMRs, and sniper rifles.

  • A Fascist Corgi

    How are they avoiding the problem of the polymer cases deforming during long-term storage? Seems to me that the obsession with reducing weight is going to end up causing reliability problems.

    • Kivaari

      Ammo in storage isn’t a new thing. Remember back to WW2 (and earlier) and the cloth belts used in the M1919 Browning machinegun held moisture and cause corrosion on the brass. To ensure more reliability soldier would open the cans and take pliers to loosen the rounds. I found a similar example on a much smaller scale. I had a TC Contender SBR, and had a survival kit with two Uncle Mikes belt slide filled with .410 shells on the shoulder straps. Leaving the rounds in the carriers while the kit sat in my gun room showed they attracted enough moisture that the brass plated steel at the base of the rounds, corroded. Then upon firing those cases would split, and needed to be driven out with a stiff ram rod. When they were set aside for a month, I didn’t expect anything like that happening. Especially when they were indoors in a heated room.

      • A Fascist Corgi

        I didn’t mean storage in ammo cans; I meant loaded in magazines. Everyone knows that box-magazine-fed shotguns are a problem because the plastic walls of shotgun shells deform over time as a result of being constantly squished by the magazine spring.

        Judging by the pictures, it looks like they have brass or copper reinforcements within the polymer shells.

        • iksnilol

          We’ll just load the magazines right before using them.


  • politicsbyothermeans

    If I had the capital and intellectual wherewithal to design a powered exoskeleton, I’d be on it like white on rice. Until then, I welcome your articles.

  • 6.5x55Swedish

    It would be nice to see the weight of every thing else the soldier carries. I suspect there are better way to shave off a few kilos.

    • Actually, no. This is one of the areas where one basic change adds up the most.

      The only other place where you could feasibly save as much or more weight in one go would be reducing the weight of body armor, which could only be done by either reducing level of penetration resistance, total coverage, or both.

      • M.S.1

        An entrenching tool weighs less, costs less, and the result of its use protects more than any body armor. But then again, digging a hole every time you stop is messy, and HQ types don’t like doing it.

  • Luke

    One thing that I have noticed is that while the weight of the weapon and the individual round of ammunition has steadily dropped from the adoption of brass cartridges to today, that the weight of the soldier’s doctrinal basic load of weapon and ammunition has stayed at a pretty consistent 16 pounds. I don’t think that an adoption of a CT weapon will change this much.

  • Greg Kelemen

    What about making every round count, mainlining smart rifle tech and those wicked Raytheon rifle launched laser guided missiles.
    It’s cost the US Army 2-3 crappy JSF’s to do, no big loss lol..

  • Jason75

    It sounds like the US Cavalry versus the Apache all over again. On the one side the US soldier loaded down with every item that command has decided he needs to survive on the plains, on a grain fed horse that needs a lot of tender loving care, versus an Indian carrying his Henry or Winchester repeater, a bag full of ammunition, and a handful of beef jerky, straddling a pony used to running all day on a few mouthfuls of grass and a few licks of water. There’s only one winner in that race.

    Cut down the soldier’s load to weapon, ammunition (lots of ammunition) helmet (WW1 showed that that is pretty vital), radio with backup batteries, and basic survival gear, and they wouldn’t be being ground down by the load they’re carrying. Light infantry needs to be light. Static positions or transported troops can carry all the other stuff, but what good is all the extra protection if the soldier is unable to perform their job of engaging the enemy?

  • M.S.1

    “7 mags or so on full auto is only a few minutes of shooting”
    Why the hell are you doing spray-and-pray in the first place, unless youre one of the guys that thinks Allah will guide the bullets?