SOME THOUGHTS ON METAL STORM
© Anthony G Williams
Last amended: August 2014
Metal Storm seems to have been around forever. I can dimly remember the first publicity clips of a box-like device firing pistol-calibre ammunition at "a million rounds per minute", and wondering what use it could be. In fact, I recall describing it several years ago as "a solution in search of a problem". However, it has evolved considerably in recent years and is worth another look.
For those unfamiliar with the Metal Storm (MS) concept, it involves stacking several rounds of ammunition in line in one gun barrel, and firing them electrically in sequence (from the front backwards, obviously!). This provides multiple shots from a single-barrel weapon without the complexity, weight, size and potential unreliability of an autoloading system. Such stacked ammunition is not a new idea, being tried in the old gunpowder days, but poor gas seals between the rounds of ammunition led to a tendency for the whole stack to go off at once. The invention of the metallic cartridge case put paid to such experiments since stacked rounds, by definition, have to be caseless. The modern caseless propellant and gas seals developed by Metal Storm are clearly secure, and the electrical firing system much simpler than the earlier efforts. It has been exhaustively tested by several military organisations and appears to be a technical success, although it has so far not entered service. Perhaps because the question still remains: what's it good for?
All manner of different MS weapons have been proposed although, ironically, few of them make use of the vaunted high rate of fire, one exception being a naval CIWS (close-in weapon system). Other suggestions have ranged from a rapid mine-scattering device to a pistol. But the current marketing emphasis is, far more realistically in my view, on grenade launchers. I say realistically because the characteristics of the MS system are best suited to short, fat, low-velocity ammunition. One of the main constraints of the system is on barrel length; the more rounds are stacked, the more of the barrel they use up and the greater the difference in the barrel length travelled by the first and last projectiles. High-velocity rifle or cannon ammunition need a lot of propellant so their rounds are very long for their calibre, meaning that you can get very few of them in a barrel. Furthermore, they generate very high gas pressure, which would stress the gas seals more. So the grenade rounds are an appropriate choice.
Metal Storm has teamed up with Singapore Technologies Kinetics (STK), one of the world's most prolific developers and manufacturers of 40mm grenade ammunition. The MS rounds basically use STK projectiles with a caseless propellant and gas seal unit fixed to the back in place of the usual cartridge case. The principal marketing focus is on low velocity (LV) rounds said to match the performance of the conventional LV ammunition (muzzle velocity 76 m/s, maximum range 400m), with three different weapons developed to use them: FireStorm, Redback and the 3GL.
FireStorm is a light vehicle-mounted system which combines four barrels, each holding four rounds. The mounting is intended to be installed on top of a vehicle and fired remotely from within, to provide close-in defence. I have to say I am dubious about this. Lightweight belt-fed automatic grenade launchers (AGLs) are available which fire far more effective 40mm high velocity (HV) ammunition and these don't run out of ammo after only sixteen rounds. Redback is a more sophisticated version of the same thing, designed to be an element in a vehicle's active defence system against incoming missiles when coupled to a very sophisticated detection and fire control suite. Here the high rate of fire is useful.
The 3GL seems to me to have more interesting possibilities. This is a single-barrel three-round unit which can either be fitted with a stock as a stand-alone weapon or attached to a rifle as a replacement for the very common single-shot underbarrel grenade launchers (UGLs). No weights or measurements have been provided so far (the MS website and publicity material are singularly uninformative when it comes to technical data) but although the 3GL is said to be light, it is clearly quite long, which is not handy if you wish to attach it to a carbine or, especially, a bullpup. It does provide three shots in a small fraction of the time it would take to load, aim and fire a standard UGL three times, which could be very useful in certain circumstances, such as ambushes (in both attack and defence). And it is unquestionably much lighter and more compact than a conventional three-round repeating launcher would be.
The first stage of development of the MS concept involved stacked rounds clipped together into modules at the factory, in which the propellant could be adjusted slightly for each round to equalise the muzzle velocities. Clipped stacks are still available, but they are not ideal for the 3GL – soldiers need to be able to "top up" their ammunition in the field, and to reload quickly and conveniently. The 3GL therefore can also be used with individually-loaded rounds – the barrel slides forwards to permit breech loading – which means that they all must have the same propellant loads. This is apparently acceptable, as the difference in muzzle velocity between the first and last rounds is said to be small.
So far so good – but I think that this concept could be developed further, to provide a primary rather than auxiliary weapon for some soldiers. The changes I envisage being needed to achieve this go in the following sequence:
1. Design a stand-alone shoulder gun without considering any UGL applications.
2. Switch from the LV to the new medium-velocity (MV) rounds (which MS is already working on). These double the maximum range to 800m, but more importantly halve the trajectory height and projectile flight time to any range, providing far greater practical accuracy.
3. The only downside with MV ammunition is the increased recoil, since the muzzle velocity is raised to 105-120 m/s. It has been calculated that a weapon firing MV ammunition should weigh at least 5 kg to reduce the recoil to a level which the average soldier will find tolerable. A typical conventional single-barrel 40mm LV launcher, with stock, weighs around 2.5 kg, give or take a bit.
4. If the weight needs to be doubled to cope with MV ammunition, then a virtue can be made from necessity by giving it two barrels. This would not only double the "magazine" capacity, it would provide the option of loading each barrel with different ammunition – say, HE in one barrel, shot or flechette rounds in the other for close-quarter fighting – with the choice between them being made at the flick of a switch.
5. Since there is no need to provide space for a reloading mechanism, there is no reason to provide a conventional stock or even a receiver. The weapon could simply consist of the two barrels (stacked one above the other), a combined breech mechanism and very short butt attached to the back end, and a skeleton framework clamped to the barrel, supporting Picatinny rails. The breech block could flip open sideways to permit reloading (and incidentally, unlike the 3GL, there would be no restriction on the length of the rounds which could be loaded). The back of the breechblock, which forms the butt, could either be thickly padded or if necessary fitted with an hydraulic recoil damper. This layout would save the weight of the stock and allow the barrels to be significantly longer while keeping the overall length of the weapon short. This would provide space for more than three rounds per barrel – at least four, and possibly up to six depending on weight considerations and possibly on the acceptable degree of variation in muzzle velocity.
6. Some other details: the Picatinny rails would include electrical contacts. This would mean that the pistol grip unit – which would include the trigger, safety, barrel selector and battery – could be attached anywhere on the underside rail to adjust the length of pull to the user's choice. The location of the forward handgrip/bipod, sights and cheek-piece could be similarly adjusted. The electrical contacts would also facilitate the addition of STK's air-burst system, using fuze setters on the muzzle.
7. Safety concerns about having the breech so close to the firer's head could be addressed not only by safety interlocks to prevent the gun from being fired unless the breech is securely locked, but also by fitting a Kevlar shield.
The potential advantages of such a weapon appear to be considerable. Compared with the obvious rivals – the six-shot revolver GLs – it would be far more compact, much faster-firing, have a larger ammunition capacity and would offer the instant availability of two different ammunition types. A tactical option, depending on the circumstances, could be to keep one barrel loaded and leave the other free to single-load specialised rounds such as flare, smoke, or video reconnaissance types. With the STK grenade range to choose from, it would be very cheap to pick any existing projectiles (including less-lethal types for riot control) and attach the MS propellant/gas seal unit to them. The use of shot projectiles – or the development of multiple flechette loadings – would provide a devastating close-quarter battle capability which, with at least eight rounds available, could make the carrying of a second weapon unnecessary. A heavy single-flechette round could also provide a useful long-range performance against body armour.
It could not replace the military rifle – each weapon has its pros and cons – but it could take its place alongside it as a very versatile addition to the infantryman's armoury.
In 2012 the original Australian Metal Storm company went into receivership. However, the US branch continues in operation and the Canadian Army is incorporating an integrated MS grenade launcher in its planning for future assault rifles. The Metal Storm website is HERE.