Come here to post or find any weapons based in design, function, or capabilities on the weapons available in the HALO Universe. I've provided my first example, and will provide more in the future.
This weapon is a top-secret assault weapon similar to the MA5 series launched in 2437. This weapon is a carbine variant firing a smaller, 5.56x45mm cartridge. It features the same bullpup alignment, in fact utilizing a near-replica of the ancient F2000 Rifle developed by humans in the 20th century. The scope has been replaced with a digital display, allowing it to be used as a weapon condition HUD or the scope itself. The scope relies on a camera at the front, integrated with NV and IR overlays. The HUD uses a magnetic compass built into the stock, a simple motion-sensing ammunition counter that resets upon placing in a new magazine, and a clock running on a 24-hour format the synchronizes to the current ship/station's time zone. The under-barrel grip has an ergonomic finger-groove design allowing for increased comfort and grip on the weapon. Implemented inside the grip are both a flashlight and red/green/blue laser dot. The laser dot uses the RGB option to optimize to the soldier's preference and/or environment, allowing for maxmimum efficiency and handiness under any circumstances. A third option for the grip/handguard is a 1-inch hole where any compatible survival knife, bayonet, or other tool may be screwed into the grip and used to better defend the user at immediate ranges. The barrel features a muzzle break with slits directed specifically upward, to reduce recoil as well as keep carbon and damage from the pointer and light. Both the pointer and flaslight are operated on the main grip, for the soldier to activate his light or pointer quickly should lights go out mid-combat, etc. With a fire rate identical to MA5B under normal circumstances, this weapon is ideal for short- to medium-range combat, or (by employing a selective-fire switch on both sides of the main grip) long-range by switching to semi-automatic and aiming slightly above your target. Should the need arise, the linear alignment of the barrel and weapon is counter-attacked by light-weight carbon-fibre rods running perpendicular to the weapon's systems and attached to the case. This strengthening of the weapon allows an ammo-less carbine to be used as an effective bat or crowbar with which to bludgeon the user's enemy or any other obstacle deemed necessary for this use. Designation XMA-ARC, release date unkown, developer unkown, manufacturer UNSC.