The XM8 rifle design featured interchangeable barrels for specialized uses. Configurations, from top to bottom: standard assault rifle w/underslung grenade launcher; carbine; sharpshooter; machine gun
Advanced Combat Rifle
Tech Level: 12
An Advanced Combat Rifle (ACR) is a generic name given to future assault rifles being developed by various governments and private manufacturers. It was also the name of a US military project in the late 1980s to design a replacement for the venerable M-16A2 assault rifle. The ACR program produced a number of design innovations that are still being disseminated into the weapon industry today. More recently, projects such as the Objective Individual Combat Weapon program continued to try and improve upon the basic design and effectiveness of front-line combat rifles. Other such projects are sure to emerge in the future. Examples of advanced combat rifle concepts developed under various programs include the Heckler & Koch G-11 K2, the Steyr ACR, and the XM8.
In recent years, many designers have generally acknowledged that modern-day combat rifles are fairly well optimized for the current level of advancement and their general design will not change drastically until radically new weapon technologies are developed. Such candidate technologies, such as electromagnetic launchers and lasers, are likely not to become viable as man-portable weapons for at least a generation, and even when they do come on-line the dominance of mainstream firearms is likely to continue for many decades afterward.
This is not to say that there aren’t still a number of avenues open for refinements and improvements in battlefield firearms. Using modern-day assault rifles as their design base, ACRs of future armies will likely be lighter, more modular, more powerful, more reliable, and will use more advanced ammunition than today’s combat rifles.
ACRs in one form or another appear in films like Starship Troopers, TV shows like Space: Above and Beyond, RPGs like Traveller, Shadowrun, and 2300 AD, and video games like Halo. The pulse rifles from the movie Aliens especially exemplify to many the general form and capabilities of a desirable ACR design.
Improved ergonomics, for easier handling and aiming, is often a major concern of gun designers. Current state of the art assault rifles (the M16A2 or the P90, for example) are already fairly well optimized ergonomically, so the basic configuration of the rifles will probably not change dramatically in the next few decades. ACRs may become shorter and less bulky for better handling by soldiers. Grips and shoulder stocks may also become more easily adjustable to better accommodate the needs of individual operators.
Weapon engineers also put a large emphasis on lightweight design. The unloaded weight for the M16A2 is about 3 kg. With advanced composite materials becoming available, unloaded ACRs will probably not weigh significantly more, even with add-ons such as underbarrel attachments or electronic sights. However, some believe that making a rifle too lightweight would make it uncomfortable to fire, possibly skewing aim and recoil absorption.
Modularity is also a major design goal. As current assault rifles are considered to be close to optimized as far as their ballistic technology is concerned, designers have instead been putting greater focus into secondary and tertiary systems attached to the rifle, such as scope, underbarrel weapons, and so on. Increasing the effectiveness and ease of use of these modular devices is one of the great ongoing concerns of advanced firearm design. Pains have also gone into making the weapon system more adaptable to changing needs. The XM-8, for instance, had interchangeable barrels that allowed the weapon to function optimally as a carbine, automatic rifle, and as a sharpshooter’s weapon.
More effective recoil compensation systems are also undergoing constant research. Improved ergonomics go quite a ways in improving this, as do adjustable stocks, padding, reworked weight distribution, and so on. Active recoil compensators, where gas venting ports or movable counterweights within the weapon are used, are already a proven technology. Steady-cam like torso harnesses, used by the heavy gunners in the movie Aliens are also being looked into.
Integrated suppressors could also prove advantageous. These are muzzle/barrel devices designed to decrease the weapon’s visual and sound signature, built into the weapon itself. Also has the advantage, touted by some concerned with soldiers’ health issues, of decreasing the incidents of hearing loss often suffered by military personnel.
A very recent development that has some future-weapon enthusiasts intrigued is the idea of electronic ignition, basically using an electrical system, as opposed to a mechanical one, to ignite the propellant of a round. This would have the advantage of giving the gun fewer moving parts, preventing much of the wear that battlefield weapons now endure, as well as increasing firing rates and easing recoil. However, concerns still exist as to electronic ignition systems’ durability and effectiveness. Research is ongoing.
There is also a trend to make ACRs much hardier and resistant to damage, as well as make them usable in the widest amounts of potentially hostile environments as possible, including in space if necessary. Precision working of the machine joints to make sure the tightest seals possible are employed, as well as advanced material construction and sealing sensitive components such as integrated electronics, can help to contribute to such features.
A caselss ACR round
A great deal of effort has gone into improving rifle ammunition. A number of different technologies have been developed in recent decades to aid in this, from exploding warhead bullets (usually abbreviated HE, for high-explosive) to mercury-tipped ammunition to teflon-coated rounds to a host of other innovations. Most of these, though in limited use here and there by both civilian and military sources, have not penetrated the mainstream of combat weapon use, mostly due to issues of cost, practicality, and politics.
However, a number of ammunition technologies were introduced specifically for use in ACRs. The most well-known of these is caseless ammunition.
Caseless rounds use a projectile surrounded by a core of intermixed primer and solid propellant held together with an advanced binding agent. This eliminates the need for metal casings, reducing bulk, weight, and cost of the ammunition.
One of the main advantages of caseless ammunition is that it simplifies the mechanical action of the rifle by eliminating the need to eject casings. This in turn reduces the weight and recoil of the weapon and allows for a greater cyclical fire rate. Caseless ammunition can also be loaded more compactly into clips, giving weapons greater magazine capacity.
Early prototypes of caseless ammunition had problems with durability and heat tolerance, but more advanced version have mostly solved these problems. In fact, in many stress tests, caseless ammunition has held up to wear and tear better than standard cased ammunition.
The main barrier to adopting caseless ammunition into mainstream military use at the moment seems to be primarily economic; it would requiring the retooling of all of a country’s small arms in its armed forces, as well as introducing new maintenance and service regimens. This is in addition to producing the ammuition itself. Many believe that caseless ammunition simply doesn’t provide that great an advantage over current conventional ammunition to justify such cost.
Another ammunition advancement being discussed for use in ACRs is carbon composite casings, bullet casings which use lightweight but very tough composites in place of the usual heavier brass and steel. This reduces both the weight and bulk of conventional ammunition, as well as allowing tolerances against higher-burning ignition charges, which can allow greater muzzle velocity and ultimately a greater penetration ability of the round. New, more powerful propellants are also being actively researched in tandem with these lighter, sturdier types of casings.
Specialized ammunition would most likely be issued to soldiers on a mission-by-mission basis. For example, if a squad were expected to encounter heavily-armored targets, they might be issued specialized armor-piercings an/or explosive rounds.
ACRs will also likely have digital ammunition counters built into them, either as a display on the weapon or wired into a soldier’s HUD or eyepiece.
Modular electronic sights are already a standard sight on modern-day assault rifles. ACRs will likely employ a low-light, infrared designator/illuminator, and telescopic all-in-one sight, made modular and easily detachable for quick replacement, calibration, or maintenance.
Future scopes will likely add more features usable by soldiers, including advanced thermal imaging, contrast enhancers, enhanced bullet-drop compensator sights, and a direct uplink to an HUD or data eyepiece. Thin fiber optics running along the barrel would also allow for around-the-corner sighting. Range, accuracy and adaptability of the sights are also expected to steadily increase as well.
Ideally, any scope or electronic sight used would also be designed with a see-through mount to allow use of the rifle’s iron sight if desired.
UNDER BARREL ATTACHMENTS
Underbarrel attachments allow a soldier to carry valuable secondary weapons and tools integrated into their primary weapon. The oldest and most famous example of an underbarrel attachment is the bayonet, still in widespread use.
One of the most effective modern underbarrel attachments is the modular grenade launcher. Most ACRs will integrate the requirement for a small (20-40mm) modular grenade launcher into the weapon’s basic design. In the US Army’s OICW prototype, the grenade launcher is fired by the same trigger as the normal ammunition, with a switch to toggle between the two functions. Other models have separate trigger systems for rifle and grenade launcher. Standard grenades currently available for use in underbarrel launchers include (but are probably not limited to):
Other underbarrel attachments already available or available in the near-future include one-shot shotgun canisters, laser designators/dazzlers, and one-shot flame projectors.
A number of miscellaneous features for future combat rifles have been bandied about. One of these is electronic recognition grips. The pistol grip of the weapon would be fitted with special sensors, so that only personnel fitting a specific thermal or biochemical signature can use it. The grips can be set for individual or multiple handprints, or to recognize signals sent to it by certain military-issued gloves.
Wireless modems built into the weapons would allow ACRs to constantly update remote sources as to their status, and allow commanders and others not on the scene to see through the weapon’s electronic scope.
Composite Casing Ammunition