NEW DEVELOPMENTS IN GRENADE AMMUNITION
© Anthony G Williams
A version of this article was published in Defence Management Journal, Issue 41, May 2008
The concept of a portable infantry weapon firing a high-explosive shell can be dated back at least to the single-shot "trench guns" of the Great War, firing low-powered ammunition of 37mm or 40mm calibre. The idea was developed further in the USSR in the 1930s, this time with automatic grenade launchers capable of firing bursts of shells. Some 40.6mm Taubin guns, which used a five-round magazine and had a range of 1,200m, were used in the 1940 Winter War with Finland, but the designer fell out of favour and his guns died with him. A separate line of development in Germany during World War 2 saw some 26.5mm flare guns provided with rifled barrels and explosive rounds. Both concepts were revived in the USA in the context of the Vietnam War, leading to two different classes of grenade launcher: those designed to be fired from the shoulder, and their more powerful automatic cousins which are mounted on tripods or vehicles. This article will look at the development and future prospects of the various types of ammunition which they employ.
The Western 40mm rounds
The first grenade round to be adopted by the US Army was in 40mm calibre, with a semi-rimmed cartridge case 46mm long. This uses a "high-low pressure" system in which the propellant is packed into a small part of the case; the gas produced on firing expands into the rest of the case before pushing the grenade up the barrel. This reduces the peak pressure and enables the rounds to be fired from light, shoulder-fired single-shot launchers, the principal example being the M79. These rounds are now mainly used in single-shot underbarrel grenade launchers (UGLs), fixed as their name suggests under the barrels of rifles. The American M203 is the most common type, but there are competitors. When the British Army decided to adopt a 40mm UGL for attaching to the standard 5.56mm L85A2 rifle, they chose the Heckler & Koch AG36 launcher, designated L17A2 in British service.
Various attempts were made during the 1960s to produce tripod-mounted automatic weapons chambered for this 40x46SR round, but it was soon realised that the performance of the ammunition was too low. A new higher-performance version was accordingly produced. This has the case slightly lengthened to 53mm, but fires a heavier grenade (240g cf c.180g) at a much higher muzzle velocity (240 m/s cf 76 m/s), extending the maximum range from 400 to over 2,000 metres. The first successful ground-based gun using this ammunition was the USN's MK19 which is still in widespread service today, although there are many competitors. Weapons in this class are known as AGLs (Automatic Grenade Launchers) or GMGs (Grenade Machine Guns) and are all belt-fed, with cyclic rates of fire typically around 300-400 rounds per minute. An AGL has recently been adopted by the British Army, again a Heckler & Koch product, the new HK40 GMG, designated in British use the L134A1.
Both 40x46SR and 40x53SR ammunition (now commonly known as LV and HV for Low and High Velocity respectively) have become NATO and indeed international standards, with many different guns from a wide variety of nations being designed to use them. The ammunition has also seen much development, with the length of the cartridge cases often varying from the nominal 46mm and 53mm.
Russia has adopted the same UGL and AGL classes of weapon, firing different ammunition. The Russian UGLs are also in 40mm calibre and have a similar performance to the Western 40mm LV, weighing 250-280g and fired at 76 m/s with a range of 400m, but fire caseless VOG-25 or VG-40 rounds (the propellant is in the base of the shell) which are not interchangeable with NATO ammunition.
The AGLs (two main types, designated AGS-17 and AGS-30) are in the 30mm VOG-17/30 calibre. This is not such as step-down in effectiveness as might be supposed, as the shell is very long and at 280g is actually slightly heavier than the 40mm HV NATO grenade and contains a similar quantity of HE. The muzzle velocity is 185 m/s and the maximum range is similar to that of the 40mm AGLs, at 1,700m for the original VOG-17 and 2,100m for the new, more aerodynamic, VOG-30. This ammunition is also available in the RAG-30 grenade rifle, which has a top-mounted box magazine and is fired from a bipod, but achieves a shorter range in this gun.
More recently, Russia has displayed a 40mm AGL, the Balkan, firing much more powerful caseless ammunition. Complete details have not yet been released, but the grenades weigh 450g and are fired to a maximum range of 2,500m.
China has adopted the Russian weapons but more recently has also developed a 35mm round for its lightweight AGLs, which has a similar performance to the other AGL rounds: 250g fired at 190-200 m/s for a range of 1,750m (on a tripod: 600m from a bipod). In addition, a 35mm caseless round for UGLs has been displayed, with a similar performance to other low-velocity UGL rounds.
A couple of special-purpose grenades worth mentioning are the Russian 30mm BMYa-31 and BS-1, intended for silent launching. The BS-1 is fired from a special sealed-piston UGL (using standard 7.62x39 or 5.45x39 blank cartridges) which traps all of the propellant gas inside, completely eliminating muzzle flash and blast. The BYa-31 differs in that it is launched using special 9x93 PMAM sealed-piston cartridges, which also emit no flash and virtually no sound on firing. The BS-1 is stated to weigh 250g and to be fired at c.175 m/s for a maximum range of 400m (200m effective) while the BMYa-31 is stated to weigh 130g and to be fired at 110 m/s for a max range of 300m. However, these figures don't really add up; with that weight and velocity, the BS-1 should go a lot further. Both are reserved for special operations forces.
The new 25mm Grenade Rounds
All of the weapons mentioned so far usually fire high-explosive fragmentation (HE/frag) grenades against personnel, with in some cases (35mm and Western 40mm) high-explosive anti-tank (HEAT) or combined dual-purpose (HEDP) ammunition being available. The HEAT and HEDP utilise a shaped-charge warhead capable (in the 40mm versions) of blowing a hole through about 90mm of mild steel or 50mm of armour plate. All types have nose fuzes triggered on impact, usually with a self-destruct mechanism.
During the 1990s the US Army became attracted to the idea of grenade-firing guns whose performance could be substantially enhanced over the 40mm weapons, partly by improving the ballistics but more significantly by introducing high-explosive air-burst ammunition (HEAB or ABM - Air-Burst Munitions) designed to explode directly over the target. This was calculated to greatly multiply the effectiveness of the ammunition against soldiers who were lying down or hiding behind cover. The penalty is a considerable increase in the complexity – and therefore cost – of both guns and ammunition. The guns require a highly sophisticated sighting, range-finding and ballistic computer system which sets the aiming mark to achieve air-burst over a specific point, calculates the projectile flight time and sets its time fuze. The special, highly-accurate time fuzes required make these grenades substantially more expensive than the simple impact-fuzed type (ten times as much, according to one manufacturer).
Two different weapon systems emerged from the US Army's air-burst grenade programme: shoulder-fired and crew-served guns, the contractors being ATK and General Dynamics respectively.
The shoulder-fired air-burst grenade gun was initially designated OICW (Objective Individual Combat Weapon) and later XM29. In that form, it combined a 5.56mm carbine with a self-loading 20mm grenade launcher with an eight-shot magazine. This combination proved unable to be reduced to its target weight, so after a rethink the 5.56mm element was deleted and the opportunity taken to increase the calibre to 25mm to allay concerns about the effectiveness of the little grenade, leading to a change in designation to XM25. The cartridge has a straight, belted case 39mm long with a muzzle velocity of 210 m/s (grenade weight not stated). Effective range against point targets is said to be 500m, with 700m against area targets. A small number of XM25 guns was despatched to Afghanistan in autumn 2010 for field-testing.
Interestingly, the South Koreans recently launched a apparent copy of the XM29 designated the K11, firing 20x30B and 5.56mm ammunition, although it appears that there has been no exchange of technical data. The grenade weighs 100g and is fired at 180 m/s, giving an effective range of 500m. The K11 was said to be on the point of entering service in 2010.
The US crew-served gun was initially known as the OCSW (Objective Crew-Served Weapon) but this was later changed to ACSW (Advanced) and was subsequently designated the XM307. This was a lightweight belt-fed low-recoil machine gun in a new 25x59B calibre, but was cancelled in 2007. However, ATK has continued a private-venture development of their LW25 Chain Gun chambered for the same 25x59B round and has developed their own range of ammunition, with more pointed noses and slightly different ballistics. The round-nosed GD grenades weighed 132g and were fired at 425 m/s, while the ATK grenades weigh 141g and are fired at 400 m/s. The effective range of the XM307 was stated to be about 2,000m (maximum 3,600m) and compared with the 40mm AGL the trajectory was much flatter; at a range of 2,000m, the 25mm grenade had a trajectory with a maximum height of 100m, compared with 400m for the 40mm HV. A semi-automatic rifle, the XM109 Barrett Payload Rifle, has also been developed to fire this ammunition, but without the air-burst technology.
|Dummy versions of ATK's range of 25x59B ammunition for the LW25 Chain Gun|
The 40mm Response: more versatile projectiles
The US Army has therefore been planning to replace its 40mm grenade launchers with far more sophisticated 25mm weapons. However, the makers of the 40mm guns and ammunition have not taken this threat lying down, and have responded with a remarkable burst of creativity. Three different air-burst systems for 40mm AGLs have emerged. One, the S418 by STK of Singapore, uses a muzzle-mounted electronic fuze-setter derived from the Oerlikon AHEAD cannon technology. Two others are by Nammo of Norway: one sets the fuze by induction while it is in the chamber and is intended for guns which fire from a closed bolt (specifically, the international CG40 Striker AGL which is in US special forces service as the MK47, the HEAB ammunition being known as the MK285), while a variation on this for open-bolt guns (such as the HK40) uses a radio signal to set the fuze when the grenade is a few metres from the muzzle. The beauty of the latter is that it can be fitted to any existing AGL without modifying the gun. The grenades are not just fitted with time fuzes, they are redesigned to distribute their fragments to the rear as well as to the sides and front, to catch targets hiding behind walls. If 25 eventually enters service it will therefore face competition from a much cheaper modification programme for 40mm AGLs, which can also fire far less expensive standard ammunition as well as the air-burst type.
The 25mm XM25 will also be facing tough competition from a more varied range of developments affecting the 40mm LV systems. These have long been available with a range of less-lethal ammunition for use in crowd control situations, generally paralleling the characteristics of the 37mm riot guns used by police forces, firing impact projectiles which may be single or multiple rubber or plastic batons, or rubber-ball shot loads. Chemical projectiles containing CS gas or similar are also available, but their use is restricted by international law to police forces. The 40mm LV launchers also have a wide variety of pyrotechnic signalling, smoke-producing and parachute-borne illuminating flare munitions made for them.
More recently, air-burst LV ammunition has been developed, with IMI of Israel working on a MultiPurpose 40mm grenade designed to be fired from a UGL modified to have an induction fuze-setter, and intended for use with the Orion sighting system which can be attached to any rifle with standard accessory rails. Arcus is also working on an airburst system. An even less expensive approach to achieving air-burst capability is offered by the two Bulgarian firms, Arcus and Arsenal, who make "jump" or "bouncing" grenades. These revive an old idea (also used by the US M397 and the Russian 40mm VOG-25P caseless) in having a small nose charge which is ignited on impact to kick the grenade back into the air where it explodes a fraction of a second later, providing a much wider fragment distribution. Arcus and Arsenal also offer "anti-diver" grenades fitted with a delayed-action impact fuze which detonates the grenade underwater, at a depth of 5 to 12m, and have a claimed lethal radius of over 10m. Video reconnaissance rounds are available from Martin Electronics of the USA (the HUNTIR) and from STK (SPARCS): these contain cameras which send real-time images back to the firer's viewer while dangling under a parachute. Finally, the extra length of some of these special-purpose rounds is being made use of to provide much bigger-capacity HE grenades, a move often combined with increasing the velocity to obtain more range, as described below.
Medium Velocity and Extended Range 40mm
The most common complaint from the users of 40mm UGLs is the lack of range and the very steep trajectory which makes hitting targets at longer ranges very difficult. Various makers are therefore offering Medium Velocity (MV) or Extended Range (ER) grenades intended for use in shoulder-fired weapons but offering significant range improvements through higher muzzle velocities and (in some cases) heavier grenades. Martin Electronics led the way with its Mercury MV HEDP round, which fires a longer and heavier grenade (containing 86g of HE compared with 32-45g for LV grenades) at a muzzle velocity of c.110 m/s, doubling the maximum range to 800m. These can be fired from suitable LV launchers, at some cost in extra recoil, but are specifically designed to work with the Rippel Effect MGL-140 six-shot revolver. Other manufacturers have followed suit, with Denel developing a 40x51 ERLP (Extended Range Low Pressure) firing a 200 g projectile at 120 m/s for a range of 800m, and Rheinmetall an MV round firing standard 240g HV grenades at 100 m/s for a range of 700m. Nammo Raufoss is also working on grenade rounds in this class. Arcus and STK, concerned about the significant extra recoil of these rounds, have developed slightly lower-performance ER grenade rounds, firing standard 165-180g LV grenades at about 90-100 m/s, giving a range of 600m.
In conclusion, grenade launchers, which were once a simple way of firing small HE shells, are becoming much more sophisticated, primarily as a result of ammunition developments (and, in the case of HEAB/ABM, highly sophisticated sighting systems). The older 40mm weapons may be bigger, heavier and ballistically inferior to the new 25mm systems, but their larger grenades provide much more versatility, especially in the LV weapons. As a result, 40mm grenades are likely to remain in service for the foreseeable future.
Grenades shown approximately to scale. From left to right: 25x39B XM25; 25x59B XM307; 40x46SR LV; 40x53SR HV; 30x29B VOG-30 (it has a more rounded fuze profile than the VOG-17); 40mm VOG-25 caseless; 35x32SR Chinese HEDP (drawing courtesy of Timothy Yan)