Why Isn’t Our Military Going 6mm? by David Crane.

Print Friendly, PDF & Email

Back in September, I wrote a quick blurb on the Chinese QBZ-95(Type 95) infantry rifle, chambered for the proprietary 5.8x42mm cartridge. Now, while it’s true that I’m not a particularly big fan of the Chinese army, it must be noted that the Chinese are not stupid, and they decided on this caliber after conducting a rather extensive amount of ballistic research and development. As it happens, our own military has been playing around with the 6mm concept for quite some time. The idea is that one 6mm round would replace both the 5.56x45mm infantry rifle round and 7.62x51mm machine gun round, and be used for both infantry rifles and light machine guns/squad automatic weapons.

The 6mm round would probably weigh between 90 and 100 grains, and utilize a cartridge case between 40 and 45mm. The basic idea is that the 6mm would give infantry rifles…

greater reach and penetration against hard targets, and it would allow machine gunners to carry more ammunition. It would also give the latter group lighter recoil than the 7.62x51mm. Supposedly, the 6mm rounds the Army has experimented with have equal or better penetration than the 7.62x51mm round at normal infantry combat distances. One common caliber would also simplify supply.

Anyway, for years, the 6mm concept has been put way back on the proverbial back burner, due to the laws of inertia and the fact that other NATO countries seem to be perfectly happy with the status quo–a status quo, by the way, that we, the United States, basically forced on them. Since then, our military has been hesitant to try to force yet another caliber of our choosing on them. However, now might just be the time. Recently, the 6mm concept has come back under the military’s radar as a result of the rather lackluster performance of the 5.56mm against Al-Qaeda forces in Afghanistan, not to mention the equally problematic effectiveness against hostile Somali gunmen in Mogadishu back in ’93. Our 62gr M855 round, hyperstabilized by a very fast 1 in 7 barrel twist rate, has apparently been zipping right through the skinny Al-Qaeda, just like it did the Somali’s, instead of yawing or going frangible inside them. It’s therefore been taking multiple rounds, as many as 4-5 rounds, to put a single man down. Needless to say, this is not what you want in a CQB scenario.

My opinion, at present, is that a common infantry rifle/machine gun round in 6mm is a good idea, provided the 6mm’s felt recoil is not problematic when fired from an infantry rifle, and the round is indeed as effective(accuracy, penetration, and wounding potential/lethality) as the 7.62x51mm GPMG round out to the edge of the envelope of average infantry combat distances. Based on my research to date, here are my thoughts on the prospective specs for a 6mm infantry round: 1) The round itself should weigh from 90 to as many as 125 grains, depending on the specific purpose intended(CQB, long range, or anti-armor) and the weapon in which it’s employed (infantry rifle or machine gun). 2) Cartridge case should be between 40 and 45mm, and should be tapered for feeding and extraction reliability. Accuracy will take a small hit(compared to a straight-cased cartridge), but reliability is always more important, especially when most combat in the future will be in urban areas, at shorter ranges. The loss of accuracy would be small anyway, provided the ammunition and weapon system to deliver it is properly designed. 3) the 6mm round itself can be either a boat-tail (FMJBT) or non-boat-tail(FMJNBT). Non-BT rounds tend to yaw more quickly and do more damage, unless the BT round is specifically designed to yaw immediately, by designing an air pocket/hollow area immediately behind the point and in front of the bullet’s core. This is what the Russians did with the 5.45x39mm AK-74 round. If we were to go with a BT bullet, we would have to design this same aspect into the 6mm. The bullet must either go into yaw quickly inside the body, or go frangible, thus destroying tissue via a different method. Otherwise, it will just plow through the target, making a clean hole in one side, and out the other–not a good thing in a CQB scenario( where your target is likely to be close enough to easily shoot back at you, before he collapses). 4) Ideally, velocity should be 2750+ fps. 2,750-3,100 fps would probably be the ideal range. Felt recoil at these velocities can be mitigated and controlled on full-auto fire if the "constant recoil" principle is incorporated into the weapon design (both infantry rifle and machine gun).

With "constant recoil", the bolt carrier never contacts the rear of the receiver, and the overall mechanism works to counter-act the recoil energy of the fired round, effectively balancing it. "Constant recoil" was invented by Jim Sullivan for the Ultimax 100 LMG, which is the lightest machine gun in the world. The Ultimax 100 is also considered by many experts to be the best LMG in the world. Like the Ultimax, the next-gen light machine gun (LMG) should definitely employ "constant recoil". On semi-auto, the weapon should fire from the closed bolt position. On full-auto, it should fire from the open bolt position, which is necessary for "constant recoil" to be effectively employed, and to mitigate the risk of cook-off. This set-up provides the best of both worlds, and is what, in my opinion, America’s next generation of infantry rifles and machine guns should employ.

Now, some would say that we have to be careful not to violate any of the limitations placed on combat ammunition by the Hague Convention. Perhaps this is a consideration. However, our soldiers, marines, and sailors should be our first priority right now. We want them to come home alive. Perhaps we should also consider this: we are fighting against terrorists right now, and it’s questionable as to whether or not we are even bound by Hague in this situation. This matter is, of course, for our politicians to decide, but they should decide quickly. American lives are at stake daily, and they should have absolutely the best weaponry at their disposal.

Why Isn’t Our Military Going 6mm? by David Crane. by

About David Crane

David Crane started publishing online in 2001. Since that time, governments, military organizations, Special Operators (i.e. professional trigger pullers), agencies, and civilian tactical shooters the world over have come to depend on Defense Review as the authoritative source of news and information on "the latest and greatest" in the field of military defense and tactical technology and hardware, including tactical firearms, ammunition, equipment, gear, and training.

Check Also

SIG SAUER MCX Reduced Signature Assault Rifle (RSAR) Suppressed .300 Blackout (.300BLK) COTS Drop-On PDW-Type Upper Receiver for QUIET Military Special Operations Missions!

B David Crane david (at) defensereview (dot) com January 7, 2023 The Firearm Blog (TFB) …