Rifts Up Close: M-31/C-40R 15mm Rail Gun

By Tim Willard

Commonly known as the SAMAS C-40R rail gun, the SAMAS rail gun has seen use all over the North American continent, as well as a myriad of other places. While the CS claims to have invented them, Bandito Arms and the Black Market know the truth, as does Triax, some adventuring groups, and even Erin Tarn once glimpsed the truth.

Originally designed in 2036 as the hand weapon of the Silver Eagle, the 15mm Rail Gun has proven to far exceed the original designers expectations. Tested by the US military at Groom Lake, the weapon went through many different configurations until finally the 15mm caliber was chosen. This caliber was light, easy to carry and manufacture, and provided excellent "armor ablative capability" when used against hardened structures.

In 2032 Colt Industries received the contract to make the next generation Squad Automatic Weapon, as well as the primary weapon of the (then) prototype SAMAS (Strategic Armored Military Assault Suit) to be fully field tested at the Groom Lake/Dreamland facility. A long time partner of the US Military and its paranoid associates, Colt Firearms did not even blink an eye when the military demanded not only the weapon, but when testing was finished, 14 micro-fabrication units had to be produced.

In 2045 the SAMAS rail gun was complete, having passed field trials at Groom Lake, and at Fort Hood Texas, as part of the Objective Force Land Warrior Project. The weapon was discussed and accepted as an acceptable replacement for the aging M2A2 General Purpose Heavy Machinegun, that had been mostly unchanged since the early days of 20th Century warfare.

The weapon, code-named Project Book of David, and listed as the XM-31, is made of advanced hyperalloys and polyceramics, with a sturdy frame designed to hold up during the rigors of combat, during high-G SAMAS maneuvers, be unaffected by the sonic shock of a firing "boom gun", light enough to be mounted on a vehicle or carried by heavy infantry cyborgs or a three man SAW team.

While many proponents of rail guns stated that the XM-31 should fire a single round, like the Boom Gun, Colt Firearms went with the ablative effect, using multiple round impacts to "sand" the armor, as well as cause micro-fractures in ion or molecularly bonded armor that were capitalized on by successive strikes by follow up rounds in the same burst. This usually caused shards of armor to be blown free of the armor plating struck by a burst from this weapon.

Comparison studies between ablative bursts and single, traditional, armor defeating rounds showed that for the smaller calibers, the burst of light rounds did more damage faster, with less resources (inlcuding rail power) than traditional rounds. However, with higher caliber weapons, the traditional armor defeating methods still won out.

The forward heat shroud is made of heat transfer resistant non-magnetic alloy, with an internal Faraday Cage to restrict "rail bleed", as well as shielding the weapon from attracting metallic ferrous debris. In addition power armor pilots and cyborgs could use the front heat shroud as an addition handgrip, much like a regular soldier would use the forward handgrips on an assault rifle.

The barrel had an unheard of 8 rails surrounding it (The CS would later drop this to 4) that accelerated the light 15mm rounds to a muzzle velocity of 4525m/s (Mach 14) which was still well short of the 11.2 km/s that a light round would require to break free of Earth orbit, thus eliminating the chance that the weapon could be used to destroy orbital infrastructure. The Chromium Guardsman weapon nicknamed the "Boom Gun" could be used to shoot down orbital structures, providing an "enhanced range" package was used. (Some accused NEMA of the elimination of the certain Brazilian satellites during the Brazilian invasion of Suriname, a claim that NEMA never disproved or acknowledged)

The chamber and feeding assembly were built of light hyperalloy, with the internal mechanisms tested for heat expansion, wear difficulties, light damage, and battlefield electromagnetic conditions. After a nuclear detonation simulation performed at Groom Lake/Dreamland the weapon was discovered to be "EM Saturated" resulting in the chamber no longer functioning correctly to "inject" the rounds into the barrel. This resulted in additional circuitry being added to create an "EM Reset" manual switch on the side of the weapon. Pushing the button discharged power into the weapons internal systems to reset them in case of EM saturation.

The chamber itself uses magnetic pressure to inject a round into the barrel, propelling it at over 100m/s into the rail accelerators, which then fling the round forward. Innovations by Colt Firearms resulted in a lowered power usage for firing. Chamber pressure could be "fixed" for the first rounds once the chamber's magnetic systems were activated, resulting in each successive round taking slightly less power until the last 10 rounds used only 23% of the energy that the first round took to inject them into the barrel. Second the magnetic pressure would be increased for a single shot, resulting in faster barrel speeds 5763 m/s for a single round. Other advances came in magnetic shielding and superconductor linings created an environment where the only thing touched by the round itself was the feeder port and the rails. This drastically reduced wear on barrel and firing mechanism parts, extending battlefield endurance and weapon part life.

The trigger assembly sported four modes. The safety mode also depended on a pistol grip safety, single shot selection, which enabled the weapon to be used to sniping against soft targets, the standard attack mode, as well as fully automatic, allowing the weapon to be used as a point defense system, anti-vehicle mode, and against massed troops. Sticking with a long tradition, Colt eschewed an electronic trigger assembly, choosing to stick with a mechanical trigger assembly that activated the various electronics. The mechanical trigger assembly proved highly effective and accurate in testing.

The stock was molded into the weapon, part of the weapon's lower receiver, and used hydraulic recoil compensation, rather than the traditional recoil spring systems in use by other companies. The hydraulic master cylinder and the hoses and additional cylinders were carefully built and shock dampened. User weapon maintenance trained to "eyeball" the hydraulics for leaking or "sweating" components, as well as having a digital pressure readout on the side of the hydraulic master cylinder.

The feed mechanism was carefully crafted by Colt Firearms, and during Groom Lake/Dreamland testing, the railgun's feeding mechanism was rebuilt nine times, and three times during Fort Hood OFLW Project. The final product was a dual loading system unlike anything originally designed.

The shells were packed in a case 40, which was attached to the belt via magnetic linkage (it required 340 psi force to break the magnetic valence bonding) that gave the belt flexibility and integrity. When the "case" was loaded into the weapon, it deposited the 40 rounds into the "pre-flight" area, which held up to 100 rounds within the upper receiver of the weapon. The casing then was ejected from the other side in two pieces. Once the rounds were deposited in the pre-flight area magnetic "bands" contained in the rounds themselves lined up the rounds in four rows of five deep and two high. Should laser/electrical inspection by the weapon's onboard computer detect a problem, the sides of the preflight chamber were magnetized, pulling the rounds apart, and then demagnetized, dropping the rounds back into the pre-flight chamber. Once the round were arranged in the "pre-flight" chamber, they were loaded into the ready chamber. The entire process, from intake of "clip" to powering up of the chamber itself, including four "rearrangements" in the pre-flight section, took less than 0.31 seconds. Misifiring of the weapon was extremely rare, and usually a case of shoddy maintenance or sabotage.

The built in scope was primarily intended for tripod/vehicle mounted weapons, but was also tied into the primary data cable to allow pilots to have a "weapon's view" window on their HUD. This allowed a SAMAS pilot to keep the crosshairs on an enemy while performing high-G manuevers, look around corners or over/under/around obstacles without exposing themselves to fire, as well as use the weapon's scope for additional "triangulation of aiming points" that brought up a pilot's accuracy by up to 5%. The scope possesses passive and active nightvision, IR, UV, VIR, and 1X/3X/5X/10X magnification. In addition the scope's sight picture could be integrated into the BaTNI in its raw data form.

Originally Colt Firearms wanted to put a hot-fusion "micropile" into the butt of the weapon, but this was cancelled after computer simulations showed that a hard impact to the stock would cause a catastrophic 236 kt explosion. Dual power conduits were built into the weapon, requiring the weapon to use an outside power source, but an emergency "energy magazine" system was built into the right side of the stock. By removing a plate on the stock, a closely pack 10 eclip wells were uncovered, in a 2x5 row, allowing the weapon user to slot standard energy weapon clips into the weapon to power it in case of emergency. Each clip was good for 5 shots.

The weapon was usually mounted on an advanced tripod system, and the M2A2 was phased out of US military arms rooms within two months. Standard doctrine called for it to be added to vehicle ringmounts, increasing the firepower of a moving convoy by nearly 150X previous estimates. Every unit outside of a medical unit had at least 1 per platoon, and infantry companies routinely carried 3-5 per platoon.

Standard doctrine called for a 4 man gunner team. One to carry the M-31 itself, one to carry the power pack and leads, a third to carry the tripod, and a fourth to carry the ammunition. Once the weapon was set up, the gunner and assistant gunner would operate the weapon while the other two provided additional fire. Most teams added two under-barrel grenade launchers for the additional fireteam members, and some infantry companies went as far as to add a missile launcher to the team, giving them heavy firepower usable in nearly all situations.

During the Cataclysm this weapon was used in nearly every role, from a squad operated weapon, to a vehicle weapon mount, to being carried by cyborgs, Mastiff's, and Silver Eagles.

During the Second Dark Ages, this weapon began being stripped down of "extra parts", usually with the BaTNI system going first, followed by the additional rails, then the "emergency energy system", and finally the "pre-flight bay".

In 32 PA, the CS began work on the SAMAS and its weapon system. The CS version got rid of the BaTNI system, the emergency energy system, and removed 4 of the 8 rails. In addition they bypassed the "pre-flight" loading system, moving directly to "tubular" internal magazine that was rear loaded by the belt system. The CS also reduced the power to the magnetic barrel pressure system. The result was a stripped down version of the original M-31 that was still combat capable and had high battlefield endurance. The CS version is 25 lbs heavier (and is the one listed for weight) and has only 2/3rds of the range, and does less damage than the old M-31 system. However, the CS suffered a lack of orbital and lunar mining facilities, as well as high-tech manufacturing abilities that were present during the late 21st Century.

The Apache Nation found one of the micro-fabricators, and have turned out the M-31's, BaTNI and all. The Black Market only ran off a few hundred of the M-31's until they could replace the M-31 schematics with the schematics of a C-40R. In addition ARCHIE-III still turns out M-31 versions when he so desires.

Weight: 98 lbs [73 lbs]
Length: 58" [55"]
Caliber: 15mm
Muzzle Velocity: 3525m/s [4525 m/s]
Maximum Range: 2000m (6000 ft) [3000m (9000 ft)]
Maximum Effective Range: 1400m (4200 ft) [2500m (7500 ft)]
Typical Combat Range: 500m (450 ft) [1250 m (3650 ft)]
Magazine Capacity: Belt Fed (Pre-flight chamber holds up to 100, usually 80 rounds, for 2 bursts and 20 single shots)
Manufacturer's Cost: 35,000 Cr [15,000 Cr]
Wholesale Cost: 70,000 Cr [50,000 Cr)
Manufacturer's Recommended Price: 110,000 Cr [Not for resale]
Black Market Price: 150,000 Cr
Wilderness Price: 25,000 Cr