And now time to examine another futuristic weapon, the XM-8. This was an offshoot of the failed XM-29 project, where some in the US Army tried to get a more direct replacement for the M-16.

The XM-8 was a carbine firing 5.56 mm rounds. No fancy caseless ammo, no airburst grenades, just bullets. The same bullets that cranky guy up the street shot in Vietnam, even. What was different here?

The XM-8 was designed to be lighter and more reliable than the M-16. Reliability would be improved in a number of ways. HK built the XM-8 around it’s highly successful short-stroke gas piston system that had been used in their G-36. The body of the weapon was entirely polymer, with easily swappable components, and design by the Udelhoven Design Studio.¹ Plus, while there were a number of ergonomic and internal design improvements over the stock G-36, they used the G-36 magazine.

Let’s talk feed devices. Recall that the original AR-15/M-16 magazine was a 20 round box magazine with no curvature. The magwell was designed to accommodate this, and is also not curved. Army desires for a 30 round magazine required some amount of curvature to accommodate the taper of the 5.56mm cartridge. But the magazine had to be compatible with all M-16s, so the top had to be kept straight. So there’s a kink in the 30 round magazine where the curved section meets the non-curved section, and this can cause problems. The G-36 magazine has a continuous taper, and is made of translucent polymer, so you can see how many rounds are left.

The G-36 is pretty “European” with a paddle magazine release, and most bolt work being done with the charging handle, which is atop the gun under the raised sight rail. It can fold to either side for ambidextrous use, and can be locked to either side for use as a forward assist. The XM-8 made some improvements here too. A shoe, sort of like what’s on an HK pistol, was added to the mag release so you could press a lever on either side of the trigger guard with your trigger finger to release the mag. Bolt release was in the front of the trigger guard. The selector was the usual ambidextrous affair, with safe/semi/full auto on the trigger group.

The XM-8 also tried to improve accessory attachment methods. Picatinny rails are expensive to machine, and add weight to the weapon and height to the accessory mount. For the same reasons that we would see the development of Keymod and Mlok in the civilian world in 2014, HK and Picatinny came up with PCAP. Just like Keymod and Mlok, PCAP uses a bunch of negative attachment points², but it was designed to totally replace Picatinny rails. Specifically, it was designed to be a superior sight attachment system. PCAP naturally mounts things in the same place each time, so sights naturally will hold zero when mounted and dismounted.

Further, the XM-8 had a new sight. The XM-8 had to be lighter than an M-16, so a sighting unit was designed to integrate a red dot sight and an infrared laser sight. This gives day/night capability in a single unit, with one battery, that’s lighter than the two separate units with two batteries and two sets of mounting hardware. Plus, the sight was synchronized so that sight adjustments to the red dot also adjusted the infrared laser sight. The military version was called the ISM-IR. If you’d like one with a visible laser sight, the civilian version is so equipped, and is the ISM-V.

Of course, then politics intervened. No army requirement was actually listed, so Congress started asking questions. HK’s competitors started asking why they hadn’t been given a shot to deliver something new if the army wanted that. Plus, some people had spent money earmarked for OICW on the XM-8, and that brought up more questions. In the end, the XM-8 was cancelled for being too expensive for what it was. At the end of the day, it was more reliable, but still fired 5.56 rounds downrange.

So what do we think? If you’re looking for a new carbine system, because you’re finally joining the 5.56 train or your previous issue carbine is old and busted and you want some new hotness, the XM-8 makes a good choice. Though, it does require new accessories because of the new attachment system.

Honestly, that might be one of the better parts of the XM-8. We really like PCAP, and we especially like the ISM-IR. That can be had in Picatinny railed form too if you want. Plus, at some point, you have to accept some development costs to get something better in the system. We’re seeing some forces go to Mlok³, and PCAP is better because it gives you a sight solution too. On the other hand, we’d really like to compare it to some of the more refined AR-15s and similar that have come out since the XM-8 program was cancelled.

Verdict: Funding Approved for program testing by the Borgundy War Department Ordnance Procurement Board

1.) They also do design work for Audi.
2.) Also known as holes. Precisely cut and aligned holes.
3.) Including Canada.

The saga of attempting to improve the effectiveness of the average infantryman continues today. Now it’s the turn of the Americans. In the late 1990s, the US Military wanted to try to replace the M-16. Again. And the conclusion of the experts was that bullet-launching technology had peaked with the M-16, and there weren’t any good ways to improve it further. So more lethality would have to come elsewhere.

Considering the problem of an enemy behind cover, the committee decided that the right answer was to have some kind of man-portable airburst munition. And this led to the design of the XM-29 OICW.¹

The XM-29 had three components. The critical one was the grenade launcher. It was a bullpup-looking affair, firing 20mm grenades from a six-round detachable box magazine. These were quite a bit smaller than everyone’s favorite 40 mm grenades, so as to be workable in a magazine, but there still weren’t many of them. Which led to the second component–the “KE Module”, which was a 5.56 carbine made by HK. It had a conventional configuration, and only an 8″ barrel. Further complicating things, the one trigger on the carbine had to also work the grenade launcher, but you had to be able to separate the two modules and use them individually (after a trigger unit was added to the grenade launcher. Plus, there was a massive thermal sight/laser rangefinder/fire control computer unit on top to coordinate the airburst over the head of the enemy. The idea was that the operator would use the rangefinder to determine range, manually program in the distance for airburst, and then fire a grenade.

Unsurprisingly, the result was big, heavy, and very expensive. Fully loaded, the XM29 weighed 8.2 kg, or a hair over 18 pounds. That’s ridiculous. It was big and unwieldy. Oh, and did I mention the cost? The XM-29 was projected to costvover $10,000 per unit. Plus, airburst grenades are roughly ten times as expensive as regular, contact-fused grenades.

All this might be forgiven if it worked. It didn’t. Oh, the carbine bit fired ok. But there were tons of problems with the airburst mechanism. And when it worked, it was judged insufficiently lethal. The 20mm round created fragments that were too small, there was insufficient explosive for a very large kill radius, and a whole bunch of fragments and energy are going to be directed upwards, away from the target. I can’t imagine that it would have been all that combat effective to have to manually program in airburst distances when enemies were firing back either.

After dumping a whole bunch of money into the airburst 20mm rounds, it was finally decided that they were unworkable. The only way to get sufficient lethality was to up the caliber. 25mm was settled on, but this would mean an even bigger grenade launcher unit. Between the ballooning weight and rapidly escalating cost, the project was terminated, and split into the XM-25 (which I’ve talked about here) and the XM-8 carbine (which I’ll talk about later).

So that’s the overview. What do we think of this project? Well, the basic concept might be sound, since I’m all in favor of raining death upon my enemies, but the execution is terrible. It would be much better if the grenade module could attach to an existing rifle to reduce costs, like the Korean K11 program. This also uses a 20 mm grenade module though, and I share the US Army’s concerns about inadequate killing capability of the 20 mm grenades.² The 25 mm grenades of the XM-25 are more effective, and a 25 mm launcher is far too big to mount on a rifle.

An even better solution would be to get airburst 40 mm grenades. There, the launchers and the grenades are already in the system. Lethality has already been proven, and there’s already cheap grenades in the system. You simply have to work out the guidance and fusing, but you’d have to do that anyway with an XM29-type weapon.

Verdict: Funding Denied by Borgundy War Department Ordnance Procurement Board

1.) Objective Individual Combat Weapon. They chose the stupidest name they could.
2.) I have no idea if the South Koreans are satisfied with the performance of the 20 mm, or if they’re banking on the enemy being unarmored, malnourished North Koreans who are also easily frightened or something.

We’re going to look at some prototype rifles that never got off the ground. First is the most exotic, the HK G11.

Back in the 80s, the Bundeswehr issued the G3. They hadn’t yet gone over to 5.56mm yet. And they noticed the classic problem of soldier marksmanship: Most soldiers are very poor shots in combat. But what to do about this problem? Automatic fire is hard to control. It can be done with sufficient training, but we’re talking about the average grunt here. A burst of three or so rounds might sound like the ticket, but subsequent shots tend to miss high and right (or left) based on body mechanics and how they interact with recoil. Consistent high right missing isn’t super helpful for getting a higher hit percentage out of a weapon. What if the burst was out of the gun before the recoil impulse got to the shooter? Three superquick rounds. That might give you the spread you’re looking for.

A brief side note: the US Army, with their cool guy M16s noticed a similar problem, and would launch a search for a similar solution, the Advanced Combat Rifle program, based on similar reasoning to the above.

So we want a burst mode that’s super quick. 2,100-rounds-per-minute quick. That’s gonna be tough. And we’re going to want regular rates of automatic fire if we set the selector to full auto. Here comes the complexity. The engineers at HK considered the problem, and decided on an enabling technology: caseless ammo.

Without that pesky case, there’s no extract/eject portion of a normal operating cycle. Less to do means it’s easier to do it all quickly. Yay! Plus, caseless ammo is way lighter than cased ammo. A gain for the logistics geeks. Plus, this would be a SCHV round: 4.73×33 mm¹. This worked to to being significantly lighter than M855 5.56. Rough back of the envelope calculations shows that for about the same weight as a G-3 and 100 rounds of 7.62×51 mm, a soldier could carry a G-11 and 500 rounds of ammunition.

Now let’s get back to America. To get adoption, the US Army wanted the ACR rifle to have a 100% higher hit probability than an M16A2. The G-11 was one of the entrants. Plus it had to be durable and reliable, etc.

A few other notes on the G-11, the rifle to fire these tiny caseless rounds. It weighed about 3.6 kg empty, had a Hensholdt unmagnified reflex sight, and a 45 round box magazine. The G-11 had integrated storage for two additional magazines for quicker reloading, sort of like the redi-mag system. It also had a bottom ejection port for ejection of misfires, or administrative clearing. You might imagine the mechanism to handle the 2,100 round per minute hyperburst plus regular full auto would be complicated and it was. And caseless made it worse. But it worked.

For the hyperburst, the barrel, firing chamber, and magazine assembly were all free floated and recoiled together. Picture a modern howitzer, except much smaller. And the nature of the mechanism meant that you’d get the three projectiles out before that recoiling assembly hit the back of the receiver, which is how they avoided transmitting the recoil for a little while.

Reloading was an interesting design too. Cartridges were in a box magazine above the rotating chamber, and were dropped in tail-first and then rotated 90 degrees into firing position. Turning a cocking lever further would dump a cartridge out the bottom if needed.

Now, let’s talk about the problems. You see, the cartridge case, that pesky bit that we deleted to cut weight and simplify the firing cycle, actually gives us a lot. For one, the cartridge case makes it easy to unload the gun. You can pull pretty easily on the rim of a cartridge case. You can’t pull easily on a compressed powder block. And you’ll want to unload it if a round fails to discharge and you need to get rid of it, or if you’re just done at the range and putting your weapon back.

The cartridge also protects all of your propellant. A cartridge case is relatively durable, and is insensitive to scratches and nicks that might arise from rough handling. It is also reasonably water resistant. No such luck for the caseless round. There were problems with damaged cases and extraction was a pain.

Further, the mechanism got weird because there’s no case to provide a seal at the back of the chamber where the firing pin is, or to seal off the barrel behind the fired bullet. Enter more complexity and a little plastic bit that went at the end of the caseless round to seal the barrel. Barrel sealing problems persisted, though.

Less obviously, the cartridge also provides a great way of getting rid of heat. A bunch of heat from firing the gun goes into heating the cartridge, not the chamber, and then the hot spent cartridge is ejected. Goodbye heat! HK had to contract with Dynamit Nobel for some special insensitive propellant that was then lacquered and used that for the rounds.

Lots of engineering and testing got these problems sorted, more or less. And here’s where the story gets vague. Depending on who you ask, there may or may not have been some thing that weren’t quite sorted. But they were sorted to the satisfaction of the Bundeswehr, who was about to adopt the G-11 in 1990, and there are plenty of documents to back that up. But then the cold war ended. Goodbye Soviet Union, goodbye scary threat, hello expensive reunification. And here the Germans decided against the G-11, which would be massively expensive. Remember, you’d have to set up new weapon and ammo production lines, and the ammo production lines would be entirely new methods. It’s not just a different size of brass/steel cased bullets. NATO wasn’t about to retool with the Soviet Union gone. So instead the Germans moved to (finally) adopt 5.56.

As for the ACR project, well, that was really more of an investigation than a serious replacement effort. And even though soldiers liked the compactness,² reliability, and capability of the G-11, and even though the G-11 exhibited a significantly higher hit probability than the M-16 (or the G-3 for that matter), it did not meet the 100% higher hit probability, and was not adopted.

Where does that leave us, then? Well, it’s time to decide how we rule on this. And the G-11 has an advantage over some of the other weapons we’ll look at in that it’s doing some things that an M-16/SCAR/whatever-5.56-carbine-you-issue-now can’t do. Namely, that fancy hyperburst, and way more ammo for the weight. Plus, since the ammo in question is square, it packs more compactly too. So there’s a logistics win and a weight of fire win. Both of which I really like. Some of the G-11K2 prototypes even were fitted with picatinny rails to mount different optics, so I don’t even have to worry about having that done.

That said, there are some concerns we’d like to put to rest. Since it’s been a while, let’s get a few LRIP guns to make sure the manufacturing process is still good, and do some high round count testing. Plus, I’d like to do some gel tests and intermediate barrier³ tests. Even if that means some projectile design updates to make the terminal effects satisfactory, I can’t forsee any major problems left.

Verdict: Approved for LRIP and phased adoption by the Borgundy War Department Ordnance Procurement Board

1.) Or thereabouts. I’ve seen some variation betwen 4.7-4.9 mm or so.
2.) Despite looking like a space 2×4, troops even liked the ergonomics
3.) Usually sheet metal and tempered glass, i.e. car parts.