(fundamentally based on the SCAR-H, though other real-world and fictional weapons are influences)
The tried-and-true M-150 family of infantry rifles, designed and primarily produced by Hellfocker Arms; action is gas-operated short-stroke piston, rotating bolt, and using an electric firing pin for smoothness of operation. Despite their antique appearance and design, the M-150 battle rifle is a ruggedly reliable weapon, simple to use and train for, made of the most modern materials. Devoid of the gadgetry and integrated computers that marked previous eras of human weaponry, the M-150 is a stripped-down rifle reminiscent of something from early 21st century, despite being made in the late 33rd. It is, however, highly modular; sensors, aimbots, smart scopes, and other attachments can be easily switched in and out, often linked to the user's HUD optics integrated into their helmets. But the weapon works perfectly fine without any bells and whistles, a necessity in harsh environments that make sophisticated electronics entirely useless or unreliable. The Terran Empire's reliance on simple, old-fashioned ballistic weapons is touted as one of many reasons for the human victory in the Great War; the M-150 is a shining example of this, having been adopted by Marine shock units in 3266 and then by the Army in 3273. It was replaced with the ICARUS assault rifle in 3278, but then re-entered service as the main infantry battle rifle in 3290 after combat experience against the Zaaroft in the Magellanic War.
The rifle has many variants, but the primary ones are the original M-150A rifle, the shortened M-150C carbine, the cut-down M-150K paratrooper carbine, and the M991 sniper rifle. The default caliber is 7.92x57mm, though the barrel and receiver is fully modular and can accept a variety of cartridges.