The French military experimented with a high-tech grenade-launcher for the same reasons the US did:
In the 1950s, the answer to the low hit probability of the average soldier at ranges higher than 100 m was the ”controlled dispersion” concept of full-auto fire, leading to the reduced-recoil 5.56 mm round.
The difficulty in implementing this concept (the recoil of the 5.56 mm round was still high enough to induce too much dispersion in a lightweight rifle), led to a shift from a burst of multiple kinetic energy projectiles to the use of a single high-explosive, fragmenting round, the fragmentation pattern taking care (at least on paper) of aiming errors.
The PAPOP project (Polyarme-Polyprojectile, similar to the US OICW) launched in June 1994 was intended to combine grenade launcher (for long range engagements) and a “kinetic energy” system for engaging targets at shorter range.
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The project did not go very far, as the weight of the combined weapon was found to be too high and the grenade carrying capacity too low.
The effective casualty radius of air-bursting grenades was also found to be very small (between 14 m² against unprotected standing target and only 4 m² against protected prone target in the most favourable case of the 35 mm grenade), and very sensitive to bursting height & grenade falling angle. All in all, it was found that in order to be effective, the detonation of air-bursting grenades needed to be triggered with an accuracy of ~1 m in both range and direction, and 0.5 m in height, an unreasonable expectation for a hand-held weapon on the battlefield.
It should be pointed out that due to their low velocity, grenades are a very different beast than bullets and that without the help of a laser rangefinder, aiming errors with a grenade launcher are a full two orders of magnitude higher than for a rifle, nearly negating all of the benefit of the large casualty radius produced by the grenade fragmentation warhead at long range.
According to US results, the typical range estimation error for trained soldiers is around 30%, so for a target at a “true” distance of 288 m (for example), even a trained soldier will hesitate between the 250, 275, 300 and 325 m setting on his grenade-launcher sight (an average miss distance of 25 m before even taking into account the intrinsic weapon dispersion, compared with a typical grenade effective radius of 5 m to 10 m), and will need to “walk his fire” to the target at range longer than 150 m, a very difficult task with single-shot grenade launchers.
Even with a tripod-mounted laser rangefinder, operated by a trained spotter in a prone position, the average range error measurement is around 5% of the distance, and could be as high as 9.3%. At 600 m range, that’s an average error of 30 m, much more than the expected casualty radius of this class of warhead.
Typical defensive hand grenades that use a very simple (compact and lightweight) fuse weigh in between 400 g and 500 g, and have a reported casualty radius of around 10 m, so it is doubtful that a 20 mm to 40 mm spin-stabilized grenade with a weight between 100 g and 200 g could achieve a much better casualty radius.
If the same range measurement error could be achieved with a hand held (or shoulder held) device, combined with a 5 m to 10 m effective radius grenade, then a 300 m practical range could be claimed, but a 600 m practical range will require the measurement error to be halved.
SPIW, OICW, and PAPOP all foundered on one major issue that the proponents apparently all just wished away: The inherent limitations of the human body that’s firing these damn things.
The ballistic solution that came out of the XM-25 program would have been great, were it fired off a tripod on full auto. Off a shoulder, semi-auto? LOL… WTF? Do these people think we have hordes of Carlos Hathcocks waiting outside the recruiting station every morning, or something…? Do they think we can manage to fire enough live ammo with those weapons to get everyone to instinctively understand the flight characteristics of those grenades, estimate ranges, and then be able to fling them around effectively under combat conditions…? At what those damn things cost?
There are inherent limitations of precision with regards to what sort of ballistic solution Johnny can actually be effective with off of his shoulder. That’s a fact of life, one which I think all too many of these programs hand-wave away. One 25mm grenade with a complex air-burst fuse in it can’t carry enough of a payload to make the whole thing work worth a damn. That’s a fact of life, inherent to the physics and chemistry involved. Just like the inherent accuracy limitations inherent to shoulder-fired weapons–Both of which militate against anything like this working with current technologies.
One other thought, here: The most likely avenue for actual improvement in what they’re calling “lethality” for the modern soldier isn’t going to be in their weapons. Those are mostly adequate-to-purpose.
Where we need help is in two areas: One, which is the continual bete noir for the budget-conscious, is in training and the provision of sufficient ammunition to do that training. The second is improvement in sighting and command/control systems.
Nine-tenths of the reason you don’t get the optimum effective fires out of your element on the ground is down to two things: One, observation–There may only be one guy who can see the enemy, or the enemy may be entirely obscured. Two, ranging–Most soldiers are absolutely horrible at assessing ranges, and that’s down to, again, inadequate training and lack of realistic training. Range estimation is something that emphatically can be learnt, but the problem is that not enough time or emphasis is put on it–Try to get a block of time on your training schedule for “Range estimation training” sometime, and you’ll see what I mean. Nobody in the senior ranks sees it as a vital issue, so it gets half-assed.
Not only that, but whatever range-finding gear you might have is hardly ever trained on or used in daily field operations. The laser rangefinder, should you be so fortunate as to have one on your MTOE, rarely if ever leaves the Arms Room, usually due to its specialized batteries not being available and/or other issues.
Even the basic stuff, like binoculars for the MG teams, are not seen as being important. You can’t use a reticle to range the target, if you don’t have one. And, the odds that if you do have one, by some accident of fate or foresight, the guy carrying the damn thing likely won’t know how to use it effectively.
The other part of all this is the bit where you spot and positively identify the enemy. You need to know what they look like, and you need to be able to spot their movement accurately, as well as ensure that you’re not actually observing friendly forces. So, situational awareness and spotting skills need a great deal of training and emphasis that they don’t normally get.
No, you want to improve this “lethality” thing, there are a bunch of other things you should be doing long before you change out your weapons: First, train better and harder. Second, procure sighting and communications gear such that you can communicate easily between members of the rifle squads about where the targets are.
“Better” weapons don’t mean squat, if you don’t direct their fires more effectively at the right targets. The low-hanging fruit here is in the training, sights, and command/control/communications/intelligence realm, not the ballistics.
They had the Cobra gunship equipped with the hand-cranked [later electrical] 40 mm grenade launcher. That was a devastating weapon in Nam.