Mass accelerator weapons are known to conserve momentum, as recoil is a significant factor limiting the firepower of such weapons. Presumably the weapon's power supply provides all of the kinetic energy of the projectile, and this method just makes the process more efficient or circumvents a limit of the technology used to provide the accelerating force. After the projectile leaves the weapon, its mass returns to normal without its velocity decreasing, which appears to violate conservation of energy. According to the codex, a mass effect field reduces the mass of the projectile, allowing it to be accelerated faster. The realism of mass accelerator weapons is dubious. Mass Effect 2 handles itself a little differently than the original Mass Effect, in that you're not going to be doing a whole lot of equipment swapping, especially in terms of armor. Larger weapons use similar principles, all the way up to dreadnought mass accelerators that fire 20kg metal slugs at over 4000 kilometers per second, so they hit like 38 KT bombs.
Mass accelerator small arms function by removing a small piece of metal from an ammunition block, shaping it into a projectile, and propelling it with a mass effect field. Because mass effect technology scales easily, mass accelerators range in size from handguns to starship weapons that run the length of the ship. Mass accelerators are common weapons in the Mass Effect setting. A mass accelerator is a weapon that uses mass effect technology to launch projectiles.
