Gravity Gun, Crowbar, Grenade and Rockets are okay. What about the Crossbow, SMG Grenade Launcher and the Pulse Rifle Main and Special, will they void the achievement?
Top Voted Answer
Sarriv answered: Although I didn't risk it with any of the weapons not mentioned in the description, my friend accidentally fired off a crossbow bolt and didn't get the achievement. As for the others, I would think pulse rifle main would void the achievement, and you won't really need the SMG grenade or pulse rifle special, because the game is surprisingly generous with grenades, rockets and explosive barrels.
Basics is, during the beginning of the game you will find your first weapon the Shotgun. You will Need this in order to exit the locked room and the padlock is on the otherside of the gate and you have to shoot it off. Once this is done, that will be your first bullet fired. You can no longer use any Gun for the rest of the game, save for the Gravity Gun, rocket, crowbar and granade.
During Act : "Low Life"
The Following Video Is A Basic Walkthrough To Get Past The Antlion Gaurdian.
There are a few videos out there on a glitch you can use, this shows the normal way to take'em down.