New Cartridge Developments and Implications for Dismounted Infantry Soldiers

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  • New Cartridge Developments and Implications for Dismounted Infantry Soldiers

    Gents,

    There has been healthy debate throughout the development of small arms in history regarding appropriate calibers and weapon designs. This is a pretty hot topic in the Grendel community since the Grendel seems to offer external trajectory ballistics that are very similar to 7.62 NATO and some of the common .308 Match loads, but out of a much smaller rifle/carbine package with significantly less recoil, and increased ammunition carrying capacity.

    That naturally has led some to propose that we could replace both the 5.56 NATO and 7.62 NATO cartridges for dismounted Infantry troops.

    I personally do not see a need to replace 5.56 NATO as it has so many advantages that are beneficial to riflemen in an Infantry Squad, however...

    I do see a huge need to replace the entire SAW/5.56 system and the M240/7.62 NATO system, since they hold squads and platoons back from being maneuverable. With the recent developments in efficient cartridge & bullet design, I think we're ready to start pushing in the direction of a new Multi-Role Light Machinegun concept with a cartridge that is smaller and lighter than 7.62 NATO, with better ballistic potential as far as trajectory is concerned.

    My reasons for not liking the SAW are many, mainly that it is way too heavy for the cartridge it fires, is unnecessarily bulky, and quite unreliable. The 5.56 NATO linked is somewhat effective at the squad level, but a slightly larger caliber would give it the power it needs.

    As for the M240/MAG58 GPMG, it is way too heavy (27.6 lbs) and long, but fires live rounds reliably and accurately. Since 7.62 NATO does not give us the ballistic performance for the weight it penalizes us with, and restricts the movement of gun teams significantly, lighter and better alternatives should be looked at. For example: the 7.62x54 PKM is one of the most common GPMGs found in 3rd World countries, weighing in at about 16.5 pounds, which is even lighter than the M249 SAW, making our enemies much more maneuverable than us.

    This is why I want a Multi-Role Light Machinegun, that would drastically enhance the maneuver capability of dismounted soldiers, making them almost as fast as their counterparts carrying M4's, while not sacrificing any of the current capabilities of the M240.

    This approach is based on balancing the individual loads of each dismounted soldier in a Light Infantry, Mechanized, Airmobile, or Airborne unit. Understanding common employment practices of Infantry Squads and Platoons requires developers to be aware that ammunition for the SAWs and GPMGs is normally cross-loaded to the Riflemen in the Rifle Squads, so that the unit can sustain itself longer if things get nasty, or Fragmentary Orders are issued after a planned mission and continuous operations kick in. A rifleman can count on carrying a 200rd drum for the SAW or a 100rd box of linked 7.62 in his assault pack, even if the SAW gunner has 600-800 rounds on his person, and the gun teams have 800-1200 rounds for the gun.

    The maneuverability penalties are painfully illustrated when a body armor-laden soldier has to shoot and move within an urban environment, as well as up in the oxygen-depraved mountains of Afghanistan. The 23lb SAW and 27.6lb M240B (without optics) are simply unacceptable in terms of weight. The Army has addressed this for Light units with the M240L, but it still only shaves off 5 pounds, making it still heavier than a PKM, and that's before you mount optics and IR pointers on it, which was standardized several years ago...so you have to have them on the gun by higher mandate.

    So, although it may not be what many are initially looking for with "fixing" the 5.56 NATO/M4 carbine, I would like to throw this topic out there for development of a new Multi-Role LMG, which requires the introduction of a new military cartridge. Here are the specs I would like to see, and I guarantee that soldiers and small unit leaders would welcome:

    1) System replaces M249 SAW and M240 machineguns for dismounts
    2) Cartridge offers ballistic improvements over 5.56 NATO in trajectory, wind drift and penetration of mud brick, cinder block, and vehicles at 500m
    3) Cartridge weighs less than 7.62 NATO, allowing at least a 20% threshold increase in ammunition carrying capacity in linked form, with an objective of 30%...without losing any elevation trajectory or penetration of equal mediums at 700m
    4) Machinegun weighs less than 11 lbs empty (threshold), with 10 lbs (objective)
    5) Overall length of LMG is no longer than an M16A2 (threshold), with 36" objective
    6) LMG uses constant-recoil operating system
    7) LMG has common mounting interface for M1913 system
    8) LMG has provisions for rugged bipod, without interfering with accessories
    9) LMG meets of exceeds MTBS/MTBF of the M240
    10) LMG has a quick barrel-change system as fast and user-friendly as M60/M249
    11) LMG has center of balance behind the pistol grip
    12) LMG has ergonomic features that facilitate most users to gain or achieve a solid sight picture without excessive neck strain

    These are some initial constraints to think about and get the discussion going. Realize that there are a lot of new nations who have entered NATO with old Warsaw Pact weapons, and many old NATO and SEATO countries who are re-looking at their small arms posture.

    LRRPF52
  • stanc
    Banned
    • Apr 2011
    • 3430

    #2
    Originally posted by LRRPF52 View Post
    3) Cartridge weighs less than 7.62 NATO, allowing at least a 20% threshold increase in ammunition carrying capacity in linked form, with an objective of 30%...without losing any elevation trajectory or penetration of equal mediums at 700m
    Ammo carry weight seems as if it should be easy to achieve. Tony Williams' envisions his proposed 6.5x45 GPC as being made from a slightly "stretched" 6.8x43 SPC case ( https://www.quarry.nildram.co.uk/The...Generation.htm ), which would give it a weight of ~280 grains. Since 7.62x51 M80 is 392 grains, the 6.5x45 ought to permit 40% more rounds to be carried.

    And, I estimate that Cris Murray's 7x46 UIAC ( https://www.thefirearmblog.com/blog/...ult-cartridge/ ) would weigh ~300 grains, which still allows 30% more ammo to be carried.

    However, it remains to be seen if the trajectory requirement can be met with (FMJ or M855A1-type) ball ammo. Also, AFAIK penetration capability of 6.5mm and 7mm ball has yet to be adequately tested.

    Comment


    • #3
      That's a good systems description!

      It also appears that you see room for a cartridge with a length equal to that of the 7.62X51 NATO.

      We should take a close look at one of Stan's long-time favorites -- the .25 Remington necked down to 6mm. One can think of it as a 6.8mm SPC stretched and necked down.

      We can analytically demonstrate that the heavier 6mm bullets will have potential from equal or better penetration than the 7.62 M80 round. The smaller diameter has an edge for getting equal sectional density bullets up to higher velocities than do the larger diameter pills. A 100-115 gr 6mm driven at the velocities this intermediate round can deliver will almost certainly be far more lethal that th 62 or 77 gr 5.56 round when similar bullet construction is used.

      Also, basing the cartridge on a stretched version of the 6.8 SPC instead of the classic .25 Remington allows about 10ksi more pressure, so performance is more readily attainable.

      Comment


      • #4
        One thing I want to point out, which many of you already know from looking at your bullet boxes, is that 6.5mm projectiles that are .264" are really 6.71mm, not like the real 6.5mm or .257". To see the difference between a 7mm, 6.8mm, and 6.71mm requires me to use calipers. I do realize that bullet weight can be increased slightly with the 7mm, but we're basically in the same ballpark. I see a slightly shorter cartridge than 7.62 NATO working well, but it really doesn't matter too much for the belt-fed weapons and existing SASS systems.

        I also have some ideas for propellant design changes that are radical, but still use existing metallic cases until the next generation of solid or telescoped cases mature, if they are not skipped by magnetic rail guns, man-portable lasers, or microwave weapons. The improved propellant could theoretically make the Grendel case capable of what a 6.5x47 Lapua does now, but I don't have a degree in chemistry, nor do I have access to the R&D facilities at DuPont.

        I would still like to see a muzzle velocity of at least 2800 fps versus 2600 fps for the LMG ammunition. When I ran my .260 AR10 with 130 Bergers in a running-gun stage at FinnSniper last year, it was really pleasant to shoot off-hand on IPSC targets wearing Russian uniform tops that were at CQB distances, and I had almost all "A"s on them using a S&B PMII on 3 or 4x. I have learned that .260 Rem has way too much case capacity for long .264" bullets loaded even to mag length, but I would also prefer a cartridge with a smaller head diameter for space efficiency for Joe to hump around.

        There are a lot of good points made by the various enthusiasts and professionals in the firearms community right now, however, I do see listings for G1 Ballistic Coefficients for longer, sleeker bullets pushed at moderate velocities and then chart comparisons against 7.62 NATO. I don't know if the G1 figures are used across the board for all the cartridges, but I and many other long-range shooters have found G1 BC data to be inferior to G7 data when looking at distances past 300m, which is where BC starts to come into play. The main conclusion the super nerds with higher math backgrounds have come to is that radar data, then G7 data are the way to go, and that BC increases with velocity.

        The threshold I would want would be a muzzle velocity of 2800fps with at least a 6.71mm projectile with a G7 BC above .215, which leans more towards 130gr bullets. M80 ball has a G7 of .198, so that is what would have to be beat by the new cartridge in mass-produced form. I lean more towards MV than expensive bullet shaping for a belt-fed gun, since cost-effectiveness for belt-fed projectiles needs to come into play. The longer 6.71-7mm projectiles will facilitate tracer use since they are long already.

        The most important things are reducing weight for the guns, and getting a lighter-recoiling cartridge, with a little gain in trajectory advantage. The calibers we're talking about seem capable of doing that right now, with FMJ's or acceptable mass-produced ammo per current guidelines.

        LRRPF52

        Comment


        • #5
          Originally posted by LRRPF52 View Post
          ...I would still like to see a muzzle velocity of at least 2800 fps versus 2600 fps for the LMG ammunition...
          I arrived at much the same conclusion from both intuitive and analytic arguments. The intuitive is based on where most of the classic full-power rifle loads are. The analytic shows that it one gets a good trajectory improvement going from 2600 to 2800 ft/sec and the added cartridge volume is much less than the change needed to go from 2800 to 3000. The trajectory improvement going from 2800 to 3000 is not particularly significant over the first few hundred meters.

          Originally posted by LRRPF52 View Post
          ...The most important things are reducing weight for the guns, and getting a lighter-recoiling cartridge, with a little gain in trajectory advantage. The calibers we're talking about seem capable of doing that right now, with FMJ's or acceptable mass-produced ammo per current guidelines...
          I gather from your earlier posts that a full-length (7.62X51 NATO COAL) cartridge is acceptable. Further, you ask that the bullet potential for penetration and perforation be at least that of the 7.62X51NATO M80 round. Most importantly, if I correctly interpreted yoiur comments, the lethality need only be intermediate between that of the 5.56 and 7.62 at all ranges.

          6mm bullets can do this from surprisingly small cartridges.

          We really do need to compare numbers against what we want the cartridge to do. Further, borrowing one of Stan's favorite refrains, we need to develop data to support or refute the analytic conclusions.

          We can do the testing with reduced loads in .243 Win, .260 Rem, and 7mm-08 cartridges. That way we can avoid the added trouble and expense of wildcatting our favorite loudenboomer.

          Cheers.

          Comment

          • stanc
            Banned
            • Apr 2011
            • 3430

            #6
            Originally posted by LRRPF52 View Post
            One thing I want to point out, which many of you already know from looking at your bullet boxes, is that 6.5mm projectiles that are .264" are really 6.71mm, not like the real 6.5mm or .257". To see the difference between a 7mm, 6.8mm, and 6.71mm requires me to use calipers.
            Umm...you're just going to confuse matters by calling 6.5mm bullets, 6.71mm. But, if you really want to go down that road, I'll point out that 7mm bullets are actually 7.21mm, and 6.8mm projectiles are 7.04mm.

            Caliber, in the US military, anyway, is generally set by the distance between lands in the rifling, not by bullet diameter. There have been some exceptions in the past -- such as the 1930s .276 Pedersen, which used .284" bullets -- but current practice is as noted above.

            Please, stick with 6.5mm, like everybody else...

            Comment


            • #7
              JASmith...Should I say Bird Dog, Oscar Deuce, Bronco, or Misty...

              Really, the most important improvement that can be realized is not necessarily the caliber, but the weight and profile of the LMG. I figure since there seem to be several options for at least duplicating 7.62 ballistics in a much smaller/lighter cartridge, why not exceed it some as well. Even if that isn't done, Joe is still left with two very heavy pigs right now that don't warrant the weight and size, so the lightweight LMG should be pursued regardless. It will also fit into the new concepts being fielded with Joint land component forces, objective warrior or whatever they call it now, and thinking of soldiers and weapons as combined systems.

              Caliber change in MG's is much easier since most western MG's have a quick barrel change system. Offering a modular system that could run on 5.56 NATO, 7.62 NATO, and other cartridges between those in size would only add to the appeal factor, but when it would be demonstrated that it could replace both linked ammunition systems for dismounts, that would turn heads.

              Biggest obstacles that I see are barrel life with hot-rodded smaller cases, finding appropriate bullets for mass-production during this major swing in demand for eco-friendly bullets, finding links for smaller than 7.62/larger than 5.56, and feed pawl geometry development and T&E. If solids are demanded by Uncle Sugar, driving bands would actually help with barrel life since there is much less bearing surface. I think John Sullivan has been looking into this lately as well, since he mentioned it in a Small Arms Review article within the past 3 years.

              Roger on the common caliber nomenclature...WILCO

              LRRPF52

              Comment

              • Tony Williams

                #8
                I am sure that such a lighweight portable MG using much lighter ammo would be very popular with the troops. What it would have to do in order to be accepted is to convince the bean counters that the advantages are worth the cost of the calibre change, compared with the lightweight 7.62mm MK48 or a PKM converted to 7.62mm NATO, as a couple of east European companies are offering.

                One detailed point on the question of bore vs. bullet diameters; the military practice is of course to use bore diameters in designations, so the bullets are always a bit larger. 5.56mm uses 5.69mm bullets, 6.5mm uses 6.71mm, 6.8mm uses 7.04mm, 7mm uses 7.21mm and 7.62mm uses 7.82mm. (Edit: I see I was beaten to this point by Stan!)

                Comment


                • #9
                  Tony,

                  Where the design for the new Multi-Role LMG would leave the others clearly in the last century would be with accessory integration. I'm doing a proof-of-concept right now in a Retro Colt Model 605 project for the assault rifle. When that's done, I will move onto the LMG. I have a ton of friends with countless machineguns in their collections, and some have 07 SOT, so I think we will eventually be able to get some things rolling. The main difference is that all the current assault rifle designs are being made without much thought being put into how many additional accessories will be required by the Pentagon to be mounted to the weapon. The M1913 rails simply don't address this issue adequately if bulk and weight are to be considered.

                  This same issue plagues the pigs more than the M4's, since they are already heavier and bulkier, and all weapons have been mandated to be Own-The-Night configured for about a decade now in many of the light Infantry and Airborne units. The capabilities are great, but the profile and weight of the components are not, especially when you see IR Illuminators/Pointers mounted on huge rails on the M240 and SAW, topped with grotesquely heavy M145 Elcans. That experience made me hate the Elcans, and I didn't even hump them...just watched my gunners do it.

                  FN seems to have a firm stranglehold on most of the US machinegun market for some reason. I would like to see more competition. Either way, there will be a market for the system I described, but I just want to see something lighter, shorter, with human interface considered for once. The ergonomics of almost every fielded machinegun design suck horribly.

                  LRRPF52

                  Comment

                  • stanc
                    Banned
                    • Apr 2011
                    • 3430

                    #10
                    Originally posted by LRRPF52 View Post
                    Biggest obstacles that I see are barrel life with hot-rodded smaller cases, finding appropriate bullets for mass-production during this major swing in demand for eco-friendly bullets, finding links for smaller than 7.62/larger than 5.56, and feed pawl geometry development and T&E. If solids are demanded by Uncle Sugar, driving bands would actually help with barrel life since there is much less bearing surface.
                    I'm sure that 6.5-7mm bullets of the type used by the military do not exist. They would need to be manufactured.

                    The same goes for machine gun links, they'd need to be designed and produced. (FWIW: links made in the 1970s for the 6mm SAW can still be had in small quantities, and they might be usable with Tony's 6.5 GPC, although originally made to fit a case of 0.012" smaller diameter. I have a couple of 6mm SAW links, and they fit 6.8 SPC cases almost perfectly.)

                    I haven't seen any indication that the military is interested in solids. The only usefullness I see for solids is for some comparative testing in the absence of true military bullets.

                    Biggest obstacles I can see are:

                    1. Getting terminal effects test data to show that the intermediate caliber truly is good enough. It seems that nobody has both the desire and the ability to do such testing.

                    2. Demonstrating the improved ballistic performance of the new caliber, probably via surrogate rounds like (downloaded) .260 Rem and/or 7mm-08, fired in, for instance, modified M60 machine gun and AR-10 DM rifle.

                    Comment

                    • Tony Williams

                      #11
                      Originally posted by stanc View Post
                      Biggest obstacles I can see are:

                      1. Getting terminal effects test data to show that the intermediate caliber truly is good enough. It seems that nobody has both the desire and the ability to do such testing.

                      2. Demonstrating the improved ballistic performance of the new caliber, probably via surrogate rounds like (downloaded) .260 Rem and/or 7mm-08, fired in, for instance, modified M60 machine gun and AR-10 DM rifle.
                      ARDEC has recently done their study on small arms calibres which concluded that 6.5mm and 7mm are better than 5.56mm and 7.62mm (using similar bullet types) but I don't know if that involved any actual testing or was just a desk exercise.

                      Unfortunately, I have heard that the powers-that-be were alarmed by the enthusiastic reaction to ARDEC's findings and are now sitting very hard on the report and refusing to talk about it...that kind of attitude is, I believe, the biggest hurdle of all.

                      Comment

                      • stanc
                        Banned
                        • Apr 2011
                        • 3430

                        #12
                        Originally posted by JASmith View Post
                        We should take a close look at one of Stan's long-time favorites -- the .25 Remington necked down to 6mm. One can think of it as a 6.8mm SPC stretched and necked down.

                        We can analytically demonstrate that the heavier 6mm bullets will have potential from equal or better penetration than the 7.62 M80 round. The smaller diameter has an edge for getting equal sectional density bullets up to higher velocities than do the larger diameter pills. A 100-115 gr 6mm driven at the velocities this intermediate round can deliver will almost certainly be far more lethal that th 62 or 77 gr 5.56 round when similar bullet construction is used.
                        Thanks for the plug, Joe.

                        While the 6mm Optimum might be worth considering, my original proposal was somewhat flawed, if only because it was based on inadequate information.

                        The first error was in postulating a VLD bullet (to maximize BC). I think Gene has noted that a VLD is a poor choice for a military bullet.

                        The second flaw was in planning for a lead-core projectile. I didn't know at the time that the US Army was later going to switch to "green" bullets.

                        An M855A1-type 6mm bullet (with 5:1 L/D) would likely weigh less than 90 grains, and have a BC subtantially lower than the 95gr lead-core VLD on which I had based the 6mm Optimum's estimated performance.

                        I might be mistaken, but it appears that eco-friendly 6mm bullets of 100-115 grains may not be feasible. The Barnes banded solid in this caliber is only 75 grains, with a 4.4:1 L/D and an unspectacular 0.341 BC. http://www.midwayusa.com/viewproduct...tnumber=950050

                        BTW, NAMMO experimented with brass solids, and found them unsatisfactory. See page 7 of: http://www.dtic.mil/ndia/2006smallarms/mauritzson.pdf Might a design like the NAMMO BNT (page 9) be what the UK would require, being it's a FMJ?

                        Comment


                        • #13
                          Originally posted by stanc View Post
                          ...An M855A1-type 6mm bullet (with 5:1 L/D) would likely weigh less than 90 grains, and have a BC subtantially lower than the 95gr lead-core VLD on which I had based the 6mm Optimum's estimated performance.
                          I get 80 grains when scaling a 62 grain bullet from .224" to .244"

                          Originally posted by stanc View Post
                          I might be mistaken, but it appears that eco-friendly 6mm bullets of 100-115 grains may not be feasible. The Barnes banded solid in this caliber is only 75 grains, with a 4.4:1 L/D and an unspectacular 0.341 BC...
                          Don't give up too soon!

                          JBM shows the 80 gr TTSX as having a length of 1.083 inches. I surmise that part of the reason for keeping the weight down is stabilization in the standard twists for 6mm rifles. Density and length both play a role in determining twist needed.

                          The Berger 115 gr VLD bullet has a bullet of length = 1.365 inches. We can get to about 100 gr by stretching the scaled M855 to this length.

                          We will need to check in more detail, but I'm pretty sure that a 100gr class "green" bullet could be made to work in a rifle with appropriate twist.

                          Remember the cardinal rule in system optimization: The optimum is always defined by the smallest thing that will work... It's frustrating for those of who are in the overkill crowd. About the only exceptions to this rule arise when packing factors allow the same number of items to be stored for the same cost as the slightly smaller one. (There is always the fiat applied by someone with sufficient authority.)

                          Comment


                          • #14
                            I gather from your earlier posts that a full-length (7.62X51 NATO COAL) cartridge is acceptable. Further, you ask that the bullet potential for penetration and perforation be at least that of the 7.62X51NATO M80 round. Most importantly, if I correctly interpreted your comments, the lethality need only be intermediate between that of the 5.56 and 7.62 at all ranges.
                            Gents,

                            I would also stipulate that the new projectile meet or exceed 7.62 NATO M80 lethality out to 600m, and exceed its penetration of standardized mediums at 500m. I'm not sure how lethality can be measured for developmental testing, since there is no scientific baseline to establish it, but I have some bullet design ideas that are multi-role, i.e.: meant to yaw in tissue, as well as penetrate hard targets.

                            The design I shared with a company in North Carolina 8 years ago peaked their interest, but I never followed up with it. It basically uses some ideas from the Russian improved 5.45mm projectile named 7N10, with a stacked cone narrow rod of tungsten or hardened steel, with a lead filler, and a uniquely shaped internal tip for the lead with a hollow nose cavity, and a thin full metal jacket with cannelure. This was for a 5.56 project, but the same thing could be applied to any larger caliber of course.

                            I would like to approach the new cartridge specs from 1) on-target performance, 2) Trajectory requirements, and 3) weight limitation constraint parameters. Then look at projectile dimensions, cartridge geometry, propellants, and links. It seems that much of the projectile theoretical and practical work has us focused on something between 5.56 and 7.62 that would be optimum, and most would agree on that. On one hand, I would really like the trajectory performance of a 7mm WSM, with the recoil and size/weight of a 5.56, but that ain't happening with what we currently have to work with. There has to be a compromise somewhere in the middle.

                            I think we can all agree that 6mm is the bare minimum in acceptable diameter to get the length/weight we need, and 7mm is probably the maximum to keep weight and recoil down, while finding the best aero-dynamic performance from a mass-produced projectile.

                            6mm offers the best terms in recoil & weight reduction and aerodynamics simultaneously, and possibly penetration and wound effects if it can yaw in tissue and fly straight through the standardized barrier mediums. It also would be easy to get to velocity, but could introduce over-bore problems for throat/barrel life.

                            The 6.5 seems to alleviate a lot of the potential drawbacks of 6mm, but poses significant challenges with regards to case capacity getting it to 2800 fps.

                            Do we all concur on this?

                            LRRPF52

                            Comment

                            • BluntForceTrauma
                              Administrator
                              • Feb 2011
                              • 3897

                              #15
                              1. Agree that the main challenge with 6.5 is MV.

                              2. Thinking about Liberty Ammunitions T3 copper body/steel tip bullets. They claim a .3 BC for a 62gr @ 3000 fps from a 20" bbl. Sectional density for a 5.56mm 62gr is around .178. SD for a 6.5mm 100 is .205 and a 107 is .219 (same as a 5.56 77gr). I'd like to explore the concept of a 6.5mm T3 with a lighter bullet for ARs and a heavier bullet for LMGs. This reflects that I'm not quite ready to give up on a unified infantry cartridge and that a lighter 6.5 bullet for ARs would help minimize the weight difference between 5.56 NATO and 6.5G, since most of the weight difference between the cartridges resides in the bullet.

                              3. Thoughts on the Knight's Armament Stoner LMG? It has constant recoil. Convert to 65G as a proof of concept?

                              4. Still think 6mm is too similar to 5.56 to change. Why not simply up 5.56 to a 90-grain projectile in a new case? Great BC and SD. Thus, I maintain that 6.5 very nicely splits the difference between 5.56 and 7.62 and that the extra bullet mass counts for . . . something! (Seriously, I'm thinking construction material barrier penetration.)

                              John
                              :: 6.5 GRENDEL Deer and Targets :: 6mmARC Targets and Varmints and Deer :: 22 ARC Varmints and Targets

                              :: I Drank the Water :: Revelation 21:6 ::

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