When I set out to work out what sort of small arms I wanted for Borgundy, I decided to start, rather sensibly, with the caliber for my infantry arms. And I was all set to write something full of hate for the 5.56x45mm NATO round and how inadequate and lame it is. But when I thought about the gun-writer orthodoxy, I started coming up with some problems. So let’s go back, and start from where we can all agree on things. Namely, World War II. The greatest of them all. First, we figured out that full-power rifle cartridges (which I’ll call ‘full power cartridges’ from here on, because I’m a lazy typist), have too much recoil energy to be fired from a normal infantry rifle (usually about 9 or 10 lbs). Somewhat satisfactory results could be achieved in the M1918 Browning Automatic Rifle, but that weighed about 24 lbs. Second, we knew that rifle cartridges possess sufficient power (for some definition of power that I’ll leave deliberately vague) to kill a man out to distances of over a kilometer. However, for most soldiers, such hits will never happen. Statistical studies showed that 90% of infantry engagements took place at ranges less than 300 meters. But why should this be? Clearly, sniper exploits would tell us that one can see much further than 300 meters in most parts of the world.

Consider that a rifle bullet will need about one second to reach a distance of 600 meters from the shooter. In that time, a reasonably fit man who is aware that he is being shot at can sprint 5-9 meters, in any direction he pleases. It will probably be from cover to cover, but we could think of this as in some random direction that would certainly be unknown to the shooter. So the chances of hitting the target at such distances are very low, unless the target is unaware or you can fill the area with bullets with your machine guns. For this reason, the Germans sought an effective range of about 500 meters or so for the 7.92x33mm round, the first of what I’ll call the “Short Rifle” rounds. This gave them a bit more range than they thought they’d need, but because they didn’t need the power of a full power round, they could make the bullet lighter and manageable on full automatic. And fully automatic fire is a great force multiplier. Submachine guns were very popular and effective weapons, but they have a very short effective range of 50m. The German StG-44 pointed a way forward, trying to bridge the gap between a service rifle and a submachine gun, and by all accounts was very successful.

After World War II, we know that NATO stuck with full power rounds with the 7.62x51mm NATO, and eventually changed over to 5.56x45mm NATO, which is a classic example of a small caliber high velocity (SCHV) round. Currently, “everyone” (or at least every chairborne commando gun-writer) says that the 5.56mm round is inadequate, and that we should move to something in the 6.5-7mm range. However, the extant examples of such rounds, the 6.5 Grendel and 6.8 SPC, not to mention the .300 Blackout, resemble the short rifle rounds with somewhat better external ballistics. Certainly as far as weight and recoil energy are concerned. Which brings up an interesting point if we look East. The Soviets adopted a short rifle round, the 7.62x39mm, shortly after WWII, as did the Chinese. If the modern 6.x proponents were correct, we’d expect at least one, but probably both of these major powers to have stuck with something similar in the short rifle round. But they didn’t. The Soviets went to SCHV with the 5.45x39mm round in the early 1970s, and the Chinese went to the 5.8×42 in the 80s. Let’s see if we can’t reason out why.

The Soviets and the Chinese would have had access to M16 rifles and their associated 5.56mm ammunition as a result of the battles of the Vietnam war, and weapons were almost certainly taken from captured stocks in North Vietnam for further study. And they found a lot to like. 5.56mm weights about half as much as full power rounds like 7.62mm NATO, and about two thirds as much as short rifle rounds like 7.62x39mm. This means that a soldier can carry more ammo for the same weight (because no one ever actually reduces the soldier’s load, despite every utterance to the contrary. Sorry S.L.A. Marshall). More ammo was a boon for the war planner. Not only does it allow units to hold a position for longer, but units that have fought through a chance contact or ambush aren’t in dire need of resupply. What’s more, smaller rounds are easier to make in bulk, and easier to ship. Perfect if you have a big army that is going to need tons upon tons of ammunition to slay the foreign devils.

Another helpful advantage is the flat trajectory that simplifies aiming at combat ranges. With the right zero, a soldier does not need to adjust his sights or his aim to be able to hit targets within combat tolerances from 0 to 300 meters, or across the practical range of the soldier. We might think that a flatter trajectory would let us get reliable hits at ranges beyond 300 meters, but this is not the case. In addition to the problems of evasive targets mentioned previously, it is very hard to distinguish targets at ranges beyond 300 meters when they do not wish to be seen. While it is easy to spot and engage nice big silhouette targets at ranges of up to 500 meters even without optical sights (see the USMC rifle qual), soldiers who are trying to live to see another day by using cover and camouflage to hide themselves are very difficult to spot at longer ranges. So the SCHV rounds make basic combat shooting easier, but they don’t remove the requirements for fancy optical sights and marksmanship skills at longer ranges.

But what about lethality? Are SCHV rounds effective enough to justify making a switch? Admittedly, I’ve sold the accounting guys already, but let’s continue all the same. Lethality is a pain to talk about, because it’s not readily derivable from a number. For small arms though, you armchair physicists out there can shut up about kinetic energy–momentum is a better zeroth-order proxy for lethality. But that’s not a very useful proxy; it’s only good if you want a number to play with. Reality isn’t nicely quantifiable–it’s complicated. Gel tests are better, especially since the no-good treehuggers will get mad at us if we try to do more pig testing. Anyway, the idea of gel (a proxy for flesh) is that we want a cavity that is deep and wide. Deep, because (if you recall your high-school anatomy course), your heart is not on the skin, and we may have to shoot through things that are in the way (arms holding a weapon in firing position, gear carried on the vest, etc.) We want it wide because we want the best chance of damaging something important, like the heart or the central nervous system. Were we civilians hunting, say, wild hogs, we’d choose a nice, controlled-expansion soft- or hollow-point bullet. This would give us great expansion and penetration, and thus plenty of dead hogs (and tasty bacon!). But soldiers are forbidden by various treaties and conventions to not use such bullets. So let’s move on. The best we can hope for is that the SCHV bullet will hit the target in such a way that it will tumble rapidly, losing velocity. If the initial impact velocity is high enough (usually, above 2,700 feet per second for most standard military ammunition) the tumbling will cause the bullet to tear itself apart. Even though this is a tiny bullet, this causes some really nasty wounds. If you can only get tumbling out of your bullet, that still makes for a big, destructive wound channel. The worst case (well, from the perspective of effectiveness–it’s still pretty sucky.), is the “ice pick” case, where the bullet goes straight through, minimizing the wound channel size.

So now we get to the historical cases. In Vietnam, complaints about the M-16 were generally about issues with maintenance. No complaints about lethality were heard–in fact the lethality was praised by the troops, and damned by the red cross. In Afghanistan, the Russian 5.45mm earned similar praise from the Soviet troops and infamy from the mujahedeen, who called it the “poison bullet”. In Somalia, and again in Afghanistan complaints started to come up occasionally about lethality issues. Now, the skeptics among you might have some issues here. Can a soldier, who may not have an optic with magnification, be sure of how many hits he scored and where? Were these hits really center of mass shots? Did he hit at all? And why were the complaints not universal? Why were some soldiers, often in the same units, totally satisfied with the performance of their 5.56 rounds? Further, in Afghanistan, many would point out the longer engagement range as further proof of the failures of the 5.56. However, the Soviets had no complaints from their 5.45mm rounds. So what’s different? Well, we have a bunch of asinine restrictions on fire support missions in Afghanistan that prevent timely assistance to infantry. And, to no one’s great surprise, eventually the enemy figures this out and exploits it with snipers attacking infantry. In Vietnam, the enemy tried to get as close as possible because they feared our artillery. We can also note two more issues with the “5.56 is crap” theory here. First, if 5.56mm was so useless at range, why would SOCOM make the Mk 12 SPR in 5.56mm? Special forces can pick their gear–why would they use such a weapon if it is so ineffective? And use it they did; SOCOM units registered plenty of long distance kills with the Mk. 12. Second, if we are using Afghanistan as our instigator for change, we’re saying that we are expecting to fight more wars in that sort of terrain. Even if I wasn’t designing a force around a conventional war, I would find this a dubious proposition. I might be more swayed by arguments in favor of preparations for urban warfare in that case–but those would almost certainly favor shorter range rounds.

We’ve established that 5.56 can be an effective round at longer ranges. Something to note here is that the choice of the bullet itself for long range shooting is a little different from the NATO usual M855. The Mk. 12 is usually used with Mk 262 rounds, which are match bullets designed for their long range performance. I’m sure the shooters among you are thinking that I’ve cheated by looking at match rounds. To them I grunt, Belichick-style. They’re missing the point. I can choose whatever rounds I want to disprove the claim that “5.56 is useless at range”. If that claim was true, then I could load whatever rounds that I please, and should get the same piss-poor results. If the argument is that using basic service rounds I’ll get poor range performance, then I would say, did you miss all of those earlier paragraphs? Scroll up, actually read them this time, and come back. I’ll wait. Bullet design is pretty important, and I’m just not a big fan of M855. Given the choice, I actually prefer Vietnam-era M193, since it fragments more reliably. M855 is sort-of-armor-piercing, with a steel cap, but not a steel core. It’s not super helpful, except for telling you which Level III plates are cheap and lame. Soft flak vests can be dealt with by just about any 5.56 with its high velocity, and hard plates will need the fancy, tungsten-cored M955. And we can totally do better than your father’s M193 with modern bullet design. Something more like M855A1 (don’t let the designation fool you–it’s really an entirely new round) or Mk. 318 SOST. The key is getting a bullet that will tumble upon impact regardless of the nature of this impact (so minimize the impact of “Fleet Yaw”), and both of these bullets do this. M855A1 also takes advantage of modern, more consistent, less temperature sensitive propellents to up the chamber pressure. We can get away with this, because said modern powders won’t dramatically increase pressure in a hot bore. I’d prefer bullets themselves that use proper lead (because the “environmentally friendly” bullet gripe is dumb), but the example is good. The point is that these are excellent examples of effective, good 5.56 rounds, and SOST has gotten rave reviews in the ‘Stan. So we can find “infantry grade” rounds that are plenty effective at infantry distances.

So now we come back to those “6.x” intermediate rounds. Specifically, I’d like to look at 6.8 SPC and 6.5 Grendel, because those actually exist. While they’re somewhat handicapped by having to fit in an M4 magazine, this means there’s no weapon weight penalty, and it keeps the ammo weight about as low as we can. However, we’re still paying quite the weight penalty–each loaded magazine weighs about half again as much as a comparable 5.56 mag (with a 30 round magazine for each case). What does this weight/higher cost of ammunition get us? Well, 6.8 SPC was designed to explicitly give us better terminal performance than 5.56, and it delivers, even when we compare modern, fancy rounds. But these modern, properly designed rounds certainly give us nothing to really complain too much about in 5.56, in a lighter, cheaper, more controllable package. So there’s no reason to switch (and SOCOM agrees with us–they’ve basically got rid of any plans that they might have had to switch over). 6.8 SPC at least delivers what it claims to out of a standard carbine barrel. Out of a long (24″) barrel, 6.5 Grendel delivers phenomenal ballistic performance, but if you put it in a regular carbine barrel, performance suffers. There are also as yet unsolved issues with stuffing a longer tracer round into that case, or trying to make it work in a belt-fed weapon. Some might say that this doesn’t matter, but if you’re actually trying to have one cartridge to rule them all and any hope of reducing weight like proponents claim (do the math though–you fail), you’ll need to replace a full power round like 7.62 NATO in the support weapon role, which means belt fed. And that’s if you buy into bulky drums for the squad machine gun–I don’t. So the Grendel doesn’t deliver the goods on a perfect intermediate cartridge round either. Are 6.x rounds good? Sure. For military use, do they have advantages over 5.56 that offset the penalties of cost and weight? No.

So, the infantry will continue to carry light, reasonably effective 5.56x45mm NATO rounds. Next, we’ll choose a carbine to launch it.