SA-71 carbine

The SA-71(h) assault carbine is designed to be the main assault weapon for space-borne humanoid troops. The (h) sub-variant has been adapted slightly to suit human physiology and responsibility level, but the ammunition and control systems are compatible with other weapons throughout the SA-70 range.

Humanoid planetary defense forces are generally equipped with the SA-72 rifle, which has a longer barrel, higher muzzle velocity, larger caliber rounds without sabots, and no energy beam or stealth capability.

The requirement to be suitable for use by space marines gave the weapon designers a priority for robustness, endurance, and to reduce recoil, because in zero-gee combat an uncanceled recoil kick will send a firer into an uncontrollable spin.

On any given day, an SA-71(h) might be shooting back at ambushers high in the jungle canopy of a hothouse world. The very next day, the same weapon might be in the vacuum of deep space, bathed in cosmic radiation and wielded by a marine encased in a battlesuit that would be his or her sole source of air, power, and ammunition for several days. The carbine has been designed to be reliable enough to cope with any environment without question.

As a result, the SA-71(h) has enormous power endurance, ammunition flexibility, and recoil absorption.

Firing options
There are three main firing modes:

Railgun.
An electrical charge is applied to superconductor rails running along the gun barrel. The rails are arranged in a helical pattern to impart spin to the round as it leaves the muzzle, thus improving accuracy. The ammunition management system supplies a round of the type selected by the firer and fits it to a sabot created on the fly from the sabot resin reservoir. The sabot ensures optimum superconductance and mechanical fit to the rails. Sabots also permit the standard kinetic round to be much smaller than the railgun caliber thus allowing ammunition cartridges to hold many more rounds.

On full power, the railgun generates enormous heat and imparts a heavy recoil force at the breech of the weapon. Providing the recoil dampening system is not overcome by sustained fully automatic fire, this energy is automatically absorbed at up to 80% efficiency, being used both to heat the reservoir of sabot resin and to recharge the weapon’s power pack. In limited-gravity environments the motors in an ACE-series battlesuit can cancel most of the remaining recoil automatically. [See ‘Effect of combat environment on SA-71(h) carbine performance’.

Beam weapon.
A phased array in the gun stock can emit lasered energy beams in the x-ray and visible bands.

The x-Ray beam'' drains such a huge amount of energy that the maximum firing rate possible is approximately one shot per hour. The advantage and disadvantage of the x-ray beam is that it has limited interaction with physical matter. It is best employed in massed volleys against very large targets such as capital ships, space stations, and ground-based targets such as'' cities — although the usefulness is reduced for ground-based targets protected by planetary atmosphere. An x-ray beam volley can have a devastating impact, or none at all. It is the most unpredictable of all weapons available to the Human Marine Corps.The visible laser beam is the most common firing option for use in vacuum. Beam diffraction limits effective range to around 20 klicks, though unhardened sensors can be dazzled at much greater ranges. To maximize power effectiveness, the laser beam will operate in low-power targeting mode until the battlesuit AI detects a hit, at which point it will automatically up the power rate to maximum. In the timeframe of the human operator’s worldview, this shift from targeting to lethal power is instantaneous and requires no human intervention.

Grenade launcher.
Specialist munitions may be slotted into the launch tube situated underneath the main barrel. Grenades are low accuracy and limited range specialist munitions powered by chemical explosive. Many Marine units are now discontinuing the grenade launcher, replacing the capability by an improved supply of specialist munitions fired through the railgun.

Assault cutters.
For close combat situations monofilament teeth can be extended from the end of the gun barrel. They can be rotated at 1000 rpm for maximum penetration. Care should be taken if the cutters are employed in a lateral, raking motion as the blades may snap off. As well as a melee weapon, the cutters have some limited capability to act as a general purpose drill or cutting tool, although the blades will blunt rapidly. Assault cutters are optimized for cutting through flesh; they are not suitable as an entrenching tool.

Effect of combat environments
Users of the SA-71 must be aware that weapon use and performance is affected by the environment.

Planetary atmosphere
Atmosphere, dust, or defensive chaff munitions can scatter an energy beam rendering it of little use except at point blank range. This scattering phenomenon is called ‘blooming’.

Planetary gravity
Most of the recoil from standard railgun kinetic dart rounds is absorbed by the recoil limiter. However, this generates enormous quantities of heat energy and sustained fire will temporarily overload the weapon’s heatsink, causing the recoil limiter to shut off until the weapon cools.

In standard use, the remainder of the recoil not absorbed by the limiter, is largely canceled by the ACE-series battlesuit, which uses the suit motors to push back against the recoil force.

This is not possible when inside a gravity well, such as at a planet’s surface, because gravity limits the technology that powers the battlesuit motors.

Where recoil is a problem, the firer may select low-power rounds, often known as ‘rocket’ rounds. A smaller charge is applied to the gun rails, which reduces muzzle velocity and recoil proportionately. Once the projectile has been ejected a safe distance from the barrel, it is accelerated by a chemical explosive. Because this second stage of acceleration takes place externally to the weapon, it creates no recoil effect for the firer. Rocket rounds are less accurate.

Stealth capability
The carbine is compatible with the ACE-2 and ACE-3 battlesuits’ stealth function, the weapon’s outside surface re-emitting an image of the view that would otherwise be obscured by the Marine and his or her equipment. The firing signature of the visible laser beam is absorbed by the suit’s heat sinks, keeping the outer surface of the weapon and the suit as cold as the external environment. In a vacuum, the laser beam is only visible if looking directly along the beam’s length i.e. only by a target under fire. Laser blooming caused by dust, atmosphere or defensive munitions will reveal the firer, as will use of any other munition type.

The stealth capability is not 100% effective against the most advanced sensors.