With the remasters of the Mass Effect trilogy in the Legendary Edition, many players are going to be jumping into the series for the first time. The Mass Effect universe is deep and fascinating, and nearly every facet of galactic culture in the Milky Way is detailed in the games' codex menus. Everything from how mass effect fields work to the cultural history of the Citadel races can be found in the codex. Mass Effect even provides players with in-universe explanations for game mechanics, including why the guns in Mass Effect 1 seemingly have infinite ammo.
The first game in the series is a bit of an outlier when compared to the two sequels. Mass Effect 1 was heavily influenced by classic RPG mechanics, which was especially prevalent in its class restrictions on weapon proficiencies. The Legendary Edition made some changes to combat which addressed some of the game's more common critiques, but the overheating weapons mechanics remains in the first game rather than more traditional ammunition systems.
The reason Mass Effect 1's weapons don't need to be reloaded is because they're not actually shooting bullets. Each firearm in the Mass Effect universe is actually a miniaturized mass accelerator. The guns use mass effect technology, the same principle behind Mass Effect's Mass Relays, to create a mass effect field around an almost microscopic projectile. Each "bullet" fired out of the gun is actually a tiny piece of metal shaved off of a block inside the weapon, which is then accelerated to supersonic speeds. This process generates a lot of heat, which then has to be vented so the gun doesn't malfunction. Technically these blocks eventually run out, but a weapon can be fired thousands of times before using up all its firepower.
Why Do You Have To Reload In Mass Effect 2 & 3?
Anyone going from Mass Effect 1 to 2 for the first time might be surprised to see that there is now a more traditional ammo counter in the corner of the screen. The second game didn't simply do away with the established canon in regards to guns, but made advancements to the lore in response to the changing game mechanics. Mass Effect 2 made significant improvements over its predecessor in regards to combat, though adding an ammunition counter still feels like an odd choice considering the way weapons worked in Mass Effect 1.
The guns in Mass Effect 2 and 3 still fire mass-effect-launched bits of metal, but the cooling process was streamlined by the addition of thermal clips to nearly every weapon. Thermal clips look like a traditional firearm magazine, but are actually detachable heat sinks that absorb the high temperatures and are subsequently disposed. With thermal clips making their way into the Mass Effect universe, a more traditional shooter experience arose, where a weapon could not be fired when out of "ammo" since there was nowhere for the gun to disperse its heat.