Mass Effect & Mass Effect 2
All modern infantry weapons from pistols to assault rifles use micro-scaled mass accelerator technology. Projectiles consist of tiny metal slugs suspended within a mass-reducing field, accelerated by magnetic force to speeds that inflict kinetic damage.
The ammo magazine is a simple block of metal. The gun's internal computer calculates the mass needed to reach the target based on distance, gravity, and atmospheric pressure, then shears off an appropriate sized slug from the block. A single block can supply thousands of rounds, making ammo a non-issue during any engagement.
Top-line weapons also feature smart targeting that allows them to correct for weather and environment. Firing on a target in a a howling gale feels the same as it does on a calm day on a practice range. Smart targeting does not mean a bullet will automatically find the mark every time the trigger is pulled; it only makes it easier for the marksman to aim.
Mass Effect 3
Modern infantry weapons are micro-scaled mass accelerators, using mass-reducings fields and magnetic force to propel miniature slugs to lethal speed speeds. Nearly every gun on the battlefield is laden with features, from targeting auto-assists to projectile shavers that can generate thousands of rounds ammunition from a small, internal block of metal.
It was long thought that personal weapons had plateaued in performance, but the geth proved all theories wrong. Mathematically reviewing their combat logs, the geth found that in an age of kinetic barriers, most firefights were won by the side who could put the most rounds down-range the fastest. But combatants were forced to deliberately shoot slower to manage waste heat, or pause as their weapons vented.
To eliminate this inefficiency, the geth adopted detachable heat sinks known as thermal clips. While organic arms manufacturers were initially doubtful this would produce a net gain, a well-trained soldier can eject and swap thermal clips in under a second. Faced with superior enemy firepower, organic armies soon followed the geth's lead, and today's battlefields are littered with these thermal clips.