XM29 OICW
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The XM29 OICW (Objective Individual Combat Weapon) was the name for a series of prototypes of a new type of battle rifle that fired 20 mm HE airbursting projectiles. The prototypes were developed as part of the Objective Individual Combat Weapon program in the 1990s. The term SABR (Selectable Assault Battle Rifle) was also used at certain points, but is less common.
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[edit] Overview
Developed by Alliant Techsystems, with Heckler & Koch as a major subcontractor, the most commonly seen version of the XM29 consisted of a semiautomatic 20 mm smart grenade launcher, an underslung assault carbine (derived from the HK G36 then in its late developmental stage) firing a standard 5.56 x 45 mm NATO round, and a top-mounted computer-assisted sighting system with integrated laser rangefinder, thermal night vision capabilities, and up to 6x optical telescopic sight. Earlier designs used different configurations and setups. A side-by-side configuration was tested before the underslung approach was adopted. Other variations included just the 20 mm launcher or one that used the MP7 rather than the 5.56 mm NATO rifle.
The launcher part has been described variously as a light semi-automatic 20 mm cannon, a grenade launcher, or an airburst weapon. It poses a classification problem, in that it does not fit neatly into any one category. On one hand, it uses much smaller shells and has a much flatter trajectory than grenade launchers. On the other, while its calibre and velocity is more similar to light cannon, it does share traits with other infantry grenade launchers.
Various problems have effectively ended the program as it was originally envisioned, including weight, bulk, and lack of effectiveness of the 20 mm airburst round. Upon cancellation in 2004, it was split into three related programs. OICW Increment One is a program to develop a family of light kinetic energy weapons, OICW Increment Two is a program to develop the airburst grenade launcher as a standalone component, and OICW Increment Three will be a program to re-integrate the two components. The XM8 was developed in an attempt to meet Increment One requirements, but has since been cancelled because the weight savings would not have been sufficient to make the XM29 workable. Instead a new program known as Lightweight Small Arms Technologies (LSAT) was begun. Meanwhile, the XM25 25 mm airburst launcher began developed to meet the Increment Two requirements. Increment Three will not be initiated until after One and Two are completed.
The OICW Increment I Request for Proposals was cancelled in October of 2005, while development of the XM25 and the OCSW program using the same 25mm round continue. It is not clear if LSAT is intended to meet the goals of OICW Increment I or if it is a stand-alone weapon system. The future of the OICW is in doubt.
[edit] Technical characteristics
The XM29 is a combination weapon, which has the 20 mm semi-automatic, magazine fed cannon/grenade launcher as its primary part, and the 5.56 mm compact assault rifle as its secondary part. Both parts are assembled into the single one-man portable unit, with the addition of the target acquisition / fire control system (TA/FCS), which is an essential part of the whole system. The XM29 is planned to become an integral part of the future Land Warrior system, capable of communicating with the other parts of this system, including the tactical computers and helmet-mounted displays.
[edit] HEAB launcher
Early in 2002 the XM29 prototypes were successfully tested with the newest 20 mm HEAB (High Explosive Air Bursting) munitions, which would be the major "kill factor" for the XM29 weapon. The launcher is capable of firing in semi-automatic mode only, and is gas operated. It has a bullpup layout with the detachable box magazine located in the butt of the weapon. The rifled barrel is used to launch the 20 mm grenades up to 1,000 meters with good accuracy. In the standard configuration most of the fire controls for the grenade launcher unit are located on the rifle unit, including the single trigger for both firing modules. It is quite possible, however, that a separate stock will be developed for the grenade launcher unit, allowing it to be used without the rifle unit attached.
The launcher has the provisions for the TA/FCS system to be mounted on its top, and the appropriate interfaces, so the data provided from the TA/FCS can be used to program the 20 mm grenade fuses. The safety and arming device/unit (SAU) used in the fuse is based on MEMS (Micro ElectroMechanical Systems) technology. These fuses have multiple function modes; including direct impact and airburst. In the latter mode the fuse is pre-programmed to detonate the warhead at a preset range, which is calculated by measuring the distance to the target (via a laser range finder) and calculating the amount of turns the projectile will make to reach that distance and feeding that into the fuse before firing. During the flight the fuse counts the number of rotations taken and detonates the warhead when the correct amount of turns has been attained. This allows the round to defeat targets without direct impact, using the blast and fragmentation effect of the high explosive warhead. The fragmentation produced by the warhead’s airburst detonation allows the attack of multiple targets with one munition and can be more deadly to the enemy than direct fire. This is a major advantage over present small arms, which in most cases require a direct hit on the target to be effective, normally only affects one target at a time and allows for greater aiming errors. Due to the warhead's forward and rearward fragmentation spread, it also makes possible the defeat of targets in defilade; in trenches, behind walls and so on. The high explosive warhead also has the advantage of not being dependent on its kinetic energy to be effective, so unlike bullets, its terminal effectiveness does not decrease with increasing ranges.
The disadvantage of this system is the extreme complexity of the electronic fuses, which results in a high price of a single round of ammunition. The plans stated that one HEAB round must cost about US $25, and it is still to be seen what the actual price of munitions will be. It is interesting that the present design of the HEAB ammunition actually has two small HE warheads at the front and at the rear of the projectile, with the electronic fuse module located between them. While the HEAB is considered a primary round for the 20 mm grenade launcher, it is entirely possible to develop a low cost anti-armour 20 mm round with a Shaped Charge warhead, which will be effective against lightly armoured vehicles (APC, MICV and like) and various hardened targets.
[edit] TA/FCS
The target acquisition/fire control system (TA/FCS) is the most expensive and complicated unit of the whole system, since it must combine day and night vision capabilities, laser range-finding unit, ballistic computer, and various interfaces to the grenade launcher and external systems. It is used to find the targets in any light and weather conditions, determine the range to the target, calculate and display the aiming data, so the grenade or bullet can be fired to the desired point of impact, and then supply the data to the grenade launcher, so the range can be preset into the grenade fuze. In the case of damage to the TA/FCS the 20 mm grenade launcher still can be used in the direct impact mode, as can the rifle part of the system.
[edit] Efficiency and cost issues
Research and testing shows that the XM29 can be up to 500% more effective than present small arms. However, the program has been effectively cancelled due to problems with cost, weight, bulk, and the lack of lethality of the airburst round. The final prototypes of the XM29 weighed in at about five and a half kilograms when empty, and nearly seven when loaded. Soldiers also complained of the sheer bulk of the weapon system. Regarding cost, some experts even commented that the idea of the XM29 "...seems to make a soldier so expensive to field that he can't be risked in combat."
