Instructions
Automatic Weapons
Find the MP5KA4 sub-machine gun in a cache on level 3, right after solving the "All-Seeing Eye" puzzle. The fully-automatic weapon works well at close-range.
Use the SCAR rifle, which you possess from the beginning, for three-round burst-fire. This weapon can also zoom for precision.
Obtain the "Strike Rifle" from fallen drones as early as level 1. The weapon offers a few firing modes, including automatic.
Get a "Hive Cannon," which you can often find on scarabs. This weapon fires explosive clusters of bugs at a fast rate.
Find the "Deatomizer mk9" in level 4 after the "All-Seeing Eye" puzzle. The weapon can burst-fire.
Obtain the "Striker" on level 6, after an "All-Seeing Eye" puzzle. The weapon uses fully-automatic firing at an extremely high rate.
Semi-Automatic Weapons
Use the pistol, which you possess at the start of the game. The semi-automatic weapon can fire as quickly as you can pull the trigger.
Find the Deatomizer mk4 toward the end of level 2, next to a fallen scientist, before you get on the train. This weapon offers a few functions, such as a charge shot, but can be used like a semi-automatic weapon.
Use the TPC Launcher, from "the Trust" weaponry, as early as level 4. The weapon fires explosive orbs, functioning like a semi-automatic grenade launcher.
Get the warp pistol in level 4 after completing the ASE puzzle toward the beginning. The weapon offers semi-automatic fire.