Resurrected Weapons: XM806 Heavy Machine Gun

The Browning M2 is nearly 100 years old, and it is still a very effective weapon. It is heavy and made with decidedly old-school manufacturing techniques. The XM806 was an effort to replace it with a newer, lighter machine gun, still chambered for the classic 12.7×99 mm BMG round. The XM806 was a development of the cancelled XM312, which was a prospective heavy machine gun that could be easily converted to fire 25×59 mm airburst grenades.

The XM806 preserved the recoil system of the XM312 (and its grenade launching sibling, the XM307). This system had the barrel and bolt move forward when the trigger is depressed, forcing recoil forces to overcome the forward momentum of both the bolt and barrel.

The XM806 weighs only 40 lbs (18 kg), less than half the weight of the M2. It has less recoil than the M2, and it’s also easier to disassemble. On the other side, it has about half the rate of fire of the M2. For present uses, a reduced rate of fire probably isn’t a huge deal. We’re long past the days of expecting a heavy machine gun to be an effective antiaircraft gun.

While the weight savings are eye-popping, one might question the point. 40 lbs is still too heavy to easily manpack, and the weapon is still very bulky. And 12.7mm BMG ammo is big and heavy. It’s going to be a bother for a team of light infantry to deploy, and they’re probably going to be better off with GPMGs supplemented by antitank weapons, not least because of the weight of the ammo. As for vehicles, the difference between 40 and 84 lbs is basically immaterial. We can mount M2s on dune buggies. We can mount M2s on aircraft and helicopters. The weight savings really don’t get us much in terms of more usability in the roles that we normally find ourselves using a heavy machine gun. And (again) we still have the weight and bulk of ammo to deal with either way, which is a much more significant issue for small vehicles.

Probably a depressing way to look at it. But the biggest thing here would be cost, and it’s really hard to compete with an established system. When the US Army cancelled the project, they diverted funds into improving the venerable M2, and I can’t fault them for it. At least the XM312 added a new capability.

Verdict: Funding Denied by the Borgundy Army Ordnance Development Board.

23 thoughts on “Resurrected Weapons: XM806 Heavy Machine Gun

  1. Checkmate

    Wonder if the KPV cartridge could be adapted for a much lower ROF gun, in order to save weight.The KPV is veeery heavy, about 10kg more than the M2A1, but also has a ROF of 1000 rounds per minute, which is excessive. I remember some dude complaining that the .50 cal was a bit “dietetic” when it came to fighting in urban environments. He was an Iraqi vet.
    What type of machine gun this would be is beyond my pay grade. Could be an upgunned M2, or something else. Would work well against drones (though for that specific application one would want the higher ROF), with a range of about 3km.
    To pitch some ideas on future reviews (shamelessly, I might add 😛 ) :
    and it’s modern day equivalent:
    Also, what might be a revolutionary weapon:
    And to ask whether a MANPAD should be shoulder launched or tripod mounted (the vast majority use tripods, such as the Mistral, RBS-70, Stardust, etc. In my opinion, this defeats their point).In the true shoulder-launched category, the king is the Stinger, though the Polish Grom has some things to say, and the Verba is an unknown. A pity the Stinger never got the AIM-9x IR sensor and block II RMP upgrade (winks to war department). Same question for ATGM’s, only the Javelin is truly shoulder-launched. Why?….

    1. parvusimperator Post author

      My problem with the KPV cartridge is weight/bulk of the cartridges and the bulk of the system to take that recoil. It’s true that in the Iraq War, coalition (ok, mostly US/UK) soldiers found the local adobe structures quite resistant to .50 cal. fire, but I’d posit the answer there involves rockets/recoilless rifles. You can get lots of penetration out of a good shaped charge, and that saves you having to deal with recoil forces. Admittedly, those are much bigger rounds, but one would use them differently. Honestly, any gun bigger than 12.7mm really really ought to be able to throw a decent amount of high explosive payload, which gets you to 20mm+. At least, for vehicular applications. Give infantry MAGs/PKMs and your choice of rocket.

      For drones, you’d want higher ROF again, yes. Or something to jam them.

      Oooh, the IWS 2000. I’ve always thought it was a clever engineering achievement, though I’ve never been the biggest antimateriel guy. And that’s a very amusing looking little bullet. takes notes

      As for tripods, well I’d say that’s the desire for more speed/range/warhead. The Javelin (which I love) is barely man portable, and that can get away with less warhead (compared to, say Kornet) with its top-attack profile. For Manpads, you can get a bigger missile with more speed and/or more range and a bigger warhead if you accept the tripod handicap. Look at the speed on Starstreak. I prefer the Stinger model there too. I’m not going to spoil any talk of focal plane arrays though. 😛

    2. Checkmate

      Forgot to ask, parvus, what do you think of the merits of disintegrating vs non-disintegrating belts/canvas belts?

    3. parvusimperator Post author

      Well, I prefer not-canvas because of the problems those run into when wet (can shrink). Otherwise, slight preference for disintegrating, but not really something I ponder much. I like the PKM a lot, and that’s non-disintegrating link. I also like the FN MAG, and that’s disintegrating link. So…kinda lower on the priorities for me. Both work well.

  2. Checkmate

    Have you heard of the Pecheneg, the latest version of the PKM? They ditched the quick-change barrel for some sort of forced-air-cooled thingy (probably back-blast operated). I’m not too sold on the concept, I’ve heard a lot of skepticism from experts, especially since the barrel change on the PKM was quite well thought-out and easy (not quite as easy as on the MG-42, but still; that mechanism was pure brilliance).
    I refer you to gun Jesus:
    That box under the gun is quite brilliant. Gives you a place to store the empty brass and belt for reuse (something not depicted but common), and circumvents the unreliability of big mags while maintaining similar portability.

    I would think about replacing the 7.62x54R with something more….modern. Right now I’m doing an amateur-esque table of possible ammo types that would fit the bill. Preferably better than the old russian, but also superior to the 7.62×51. My list is:
    300 Win Mag (could be waaaay too powerful)
    300 Lapua Magnum (ditto x2. Also known as the Bat out of Hell. Suffers from vaporware syndrome)
    7.55×55 Swiss (arguably the best caliber to come out of WW2, but strange)
    .284 Winchester (the sporter’s friend)
    6.5 Creedmoore (Grendel’s big adopted brother)
    6.5 Grendel itself (though I would prefer it to be the battle rifle caliber in use, it does have good range quality.Less than the Creed, and the ability to use the same cartridge is not bad. I haven’t a clue whether the bullets themselves are interchangeable).
    Those last 3 are the most technologically advanced of the bunch. Honorary mentions go to the 6.5×47 Lapua (those dammed Finns build their guns out of adamantium) and the 7×64 (very popular sporting ammo around these parts, but unlikely for you to have experience of it:
    Alas, since I live in the socialist paradise, I can’t get hand’s on experience with these cartridges. But perhaps you might (or, at least, know someone who does. Some of them are high-end and expensive).

    1. Fishbreath

      parvusimperator wrote (very) briefly about the Pecheneg here.

      I have a K31 that I quite like. The 7.5×55 Swiss cartridge dates back to the dawn of the rimless cartridge era—the Swedes and the Spanish beat the Swiss to the idea, but only by a little bit, and the surplus ammo in my gun safe is in the same pattern as the issue ammo as of 1911. (I haven’t taken it to the range lately because I’m running low on GP11, and it’s getting harder to find surplus.) While it is a much more modern cartridge in design, I don’t know if it performs well enough to make an upgrade worthwhile.

      I love the idea of 6.5 Grendel, but other firearms projects have gotten in the way, and I haven’t put together my rifle yet. No firsthand experience there.

    2. parvusimperator Post author

      I kinda like the PKM, and suspect that quick-change barrel isn’t all that much needed lately. But I would like statistics and operations research or something to back that up. That said, the PKM is pretty light already.

      Well, what are you dissatisfied with in the 7.62x54R, and (more importantly) what prices are you willing to pay to fix those. I’m not thrilled with it being rimmed, since it’s a lot easier to design reliable semiauto and belt-fed automatics with rimless, but there are good working designs for it right now.

      As for 7.62x51mm, I’m pretty happy with it in the roles its expected to fill in the US Army/USMC and the balance of ballistics, weight, recoil energy, etc. that it has. Plus, there are good projectile designs available, a big logistics tail of cartridges and suppliers ready to go, and plenty of reliable, proven weapons to use it. Were it up to me, I would spend money on other things and stand pat on 7.62x51mm.

      .300 Win Mag is waaaay too powerful for the GPMG cartridge role. It makes an excellent sniper’s cartridge though, and is in use by American forces for some dedicated sniper rifles with big optics. It’s also fun if you like things that are big and loud, or have the range space to stretch some legs.

      Fishbreath already commented on 7.55×55 Swiss, so I’ll leave that to him. 6.5 Creedmore is the other one that stands out to me, because the in-flight ballistics are better than that of 7.62×51. We’re starting to see some semiautos chambered for it (there’s an M1A (read: Civvie M-14), as well as some AR-10 type rifles in 6.5 Creedmore that were at SHOT show this year). But I don’t know if anyone’s got it running well in a belt fed. You could do a conversion, but I personally wouldn’t bother.

      In a bolt gun though, 6.5 Creedmore is pretty sweet if you have a nice long range to play in.

    3. Checkmate

      The reason I’m looking into replacing the 7.62R is due to the recent concern the US Army and USMC have with overmatch in range. Basically, where yesterday the max range was 300m, today they want something that could touch stuff out to 600m(they actually want more, but I\m being conservative; anything else is wishful thinking). That puts the GPMG in an awkward role, or rather eliminates it’s role, so one would want something that could shoot out to between 600 and 1000m, with volume effects further out.

    4. parvusimperator Post author

      Let’s be careful here. 7.62x54R has similar ballistics to 7.62x51mm NATO. Similar bullet weights at similar muzzle energies. Both should be effective to 1,000+ meters at least.

      7.62x39mm is designed for the close fight, and it’s arc-y trajectory makes it hard to use past 300m.

      All that said, I think the US Army/USMC ideas of “overmatch” are dumb, and that our current caliber choices (and the roles that they fill) are fine. YMMV, of course.

    5. Checkmate

      And you would be correct if one refers to the US. However, a small nation requires any advantage it can get. Neither the 7.62R nor the 7.62N is boat-tail. Nor do they benefit from the massive advances in computational power that have allowed a better understanding of fluid dynamics in recent years (which is why the Grendel, Creed and Lapua are as dammed accurate as they are). These changes are bound to happen , so why not be the first to implement them?
      The big problem then becomes soldier load, but I won’t go into detail since that topic is vast. And I still haven’t found a good diagram of the Grendel and Creed bullet geometry to see if they be interchangeable (not the cartridges, just the bullets; yes I know they come from very different backgrounds but seem very similar; the angular differences in the cone and shoulders is minute; if you can use the same bullet for both the GPMG and the rifle, even in differing cartridges, it eases logistics).

    6. parvusimperator Post author

      Soldier Load! That’s always one of my concerns. You’ve probably seen me babble about it here. Though, you might be able to get a bit of improvement if you switched from 7.62R/N to 6.5 Creed. Maybe. I don’t recall the weights that well. It’s probably my biggest reason not to go from 5.56/5.45 to any bigger cartridge. That, and more performance there isn’t going to help most troops.

      why not be the first to implement them? Shrug. Cost maybe? There are lots of other things to spend the money on. And maybe a small nation should spend it on bullets, or maybe on NVGs. And I’m not actually sure if the better rifles outweighs having commonality with a bigger ally. Probably depends on how well you trust said ally, right?

  3. Checkmate

    Ack, the more I look into these things, the more my head throbs…. Basically, I’m asking myself whether the SAW is necessary once you have a light GMPG and a somewhat heavier weapon. What the SAW does is bring more automatic firepower, but that is because the M4 was rather lacking in this area (while controllable, it’s light barrel made sustained firepower a problem. Not much material to soak up heat). It was a patch for a problem that should not have existed in the first place, and it is no coincidence that the slow removal of the SAW coincides with the introduction of the heavier profile M4A1. If you have the lighter PKP-ish weapon closing in from the top, and the heavier assault rifle from the bottom, the SAW loses most of it’s role. I think the Marine corps knows this, which is why it’s experimenting with the M27 in general use. Important to note that when used with a heavier weapon the accuracy of a given round increases due to the stabilizing effect of the weapon. One wonders if your GPMG/LMG can’t also be used as a DM rifle with the right optics (optics is the reason this doesn’t happen reqularly; both the PKM and the M249 are way more accurate than their sights permit).
    When one refers to soldier load, one must understand the conditions: mechanized infantry have less of a problem. Light infantry (marines, alpine troops, paratroopers, etc) is expeditionary in nature (well, except alpines), and not something a small nation should focus on. Long-range light patrols, or on foot, through hostile territory (so you need to carry most of your gear with you) is not something a defensive posture uses. It’s something that became significant in the post-9/11 conflicts in Afghanistan/Iraq/etc due to the vast territory and expeditionary nature of these conflicts. A place like Poland or Slovakia or Bourgundy doesn’t need strong emphasis on that, which means more on achieving overmatch through cutting provisions for long-range patrols. They’d be fighting near their bases either way. In that regard using the Grendel for the infantryman and the Creed for the GPMG/DM role works out better.
    Yeah, the US is a great ally to have, however the US itself is thinking of shifting paradigms (polymer cased ammo, telescopic ammo, 6.5/6.8 fest, M27 fest, etc). And is also 3000km away….
    PKM barrel and gas system, MAG58 (M240) feed style with flexible ammo bag.

    Side note: a heavier weapon would help deal with the problem of strong recoil generated by use of a rifle grenade similar to the APAV40 and AC58 of the french Famas. Add a alidade to the siderail and you have light mortar, without the need to carry one of those commando mortars. An APAV40 generates about as much energy as a .50 BMG for a range of 1000m, which is why it kicks like a dammed mule when used in an assault rifle. When used in a weapon twice the weight, the thing becomes more manageable (and the weapon itself is much sturdier). Simply flip the alidade so that it normally points downwards when the GPMG is used as a GPMG, and up when it’s used to launch those projectiles (the anti-tank is less useful, but the frag and thermobaric are killers).
    Now your gunner is also your light mortar man and designated marksman (though different squads would use them in one specific role; it’s a flexibility, and depends on the conditions on hand). I’m not refering to the infantry assigned to armor, which would use IFV’s, but regular infantry, which is more likely to use APC’s and would benefit from such firepower.
    And in case you wonder why it should do this the answer is: because WHY THE HELL NOT?

    1. Checkmate

      Though one wonders how soldiers coped with loads in the 50s, when the 7.62N was the mainstay for the M14 and FN FAL…less ammo? Less protection? More vehicular transport? Different doctrine?…

    2. parvusimperator Post author

      Less ammo and less protection. Protection was a steel helmet only. US Army introduced flak vests (soft armor, can take 9mm and fragments only) widely in the 60s. I don’t think those became widespread in other armies until the 80s, though I have less information on them. I know Soviet flak vests started becoming a concern for NATO in the mid 80s.

      And yes, less ammo was carried as well. IIRC the ‘by the book’ basic load when the M14 was standard issue was one mag in the gun plus four on the body, for a total of 100 rounds. Your mileage may vary, soldiers may carry more. I think FAL loads were similar, at least “by the book”.

    3. parvusimperator Post author

      Why not? The best answer, haha!
      And yes, M4A1 has a heavier barrel than the M4. And it’s heavier in the proper place, under the handguard. The HK416/M27 has a barrel that’s even heavier still. Honestly, that’s probably the best part of the HK. If I recall correctly, it’s a different steel as well, but I forget which.

    4. parvusimperator Post author

      I would also point out that the USMC has found the M27 (with appropriate optics choice) is acccurate enough to be a DMR. They really like it. Gee, almost like a free floated barrel is a good idea…

      Given that the US is playing “she loves me/she loves me not” with new weapons/calibers/ammo, that might also be worth waiting out. I would hate to make a big buy of something new, only to have America buy something different (cf. the .280 British). But that’s me, I’m boringly conservative a lot of the time.

      As for light GPMGs, well, coming attractions (since I don’t have enough to write a proper article yet, this was just demoed). But you will like this:

      7.62x51mm. 6 kg. You’re welcome. 🙂

    5. parvusimperator Post author

      Also, the Germans thought that in most circumstances, the STG-44 was fine in the squad and no MG-42 was required. I’ve summarized their arguments here, or you could go buy Collector Grade’s Sturmgewehr.

    6. parvusimperator Post author

      And one more thing. There’s a discussion in here of differing M4 variants and the HK416 and how long they stand up to cyclic rates of fire that you might find interesting. Alas, I don’t have this data for more weapons.

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