Warhammer 40,000: Space Marine
35 Achievements
Burn Them All
Complete a Chapter of the single-player campaign using only Plasma weapons.
0.7%
How to unlock the Burn Them All achievement in Warhammer 40,000: Space Marine - Definitive Guide
Just use your plasma pistol (No melee or grenades), and only kill required enemies until the objectives appear (press B on the control station, and again to grab the power source.) Use full charge pistol blasts on the two big orks, and keep rolling out of their reach until they drop.
This will end the mission very quickly, and provide you with the achievement.
Enjoy!!!
Just play Chapter 10 on easy (the chapter with the sentrys).
Switch to your Plasmagun and play. Don't use grenades or melee.
The achievement should pop up when you get out of the elevator.
You'll receive the Plasma Pistol during chapter 6 and the Plasma Rifle during chapter 12. You can, however, get this during chapter 7 - but you'll only be able to use the Plasma Pistol. I'd recommend playing on easy for this, so you'll have a better chance at surviving.
Another great place for this (thanks to c1ned1ne) is chapter 14 on Easy. There will be weapon crates at the front of it to choose what you want to do. When doing chapter 14 on easy, you get just enough ammunition to not miss and still be able to do this. The hardest part will more than likely be when you fight the two Chaos with the Daemon Mauls. DO NOT USE MELEE, EXECUTIONS, OR GRENADES.
A good place for this is in chapter 10 since it has mainly turrets which can be easily taken out with the Plasma Pistol. Thanks InfiniteStates
The Plasma Pistol is obtained in the manufatorum, during Chapter 6. The Plasma Gun can be found during chapter 12. This achievement can be gained as easily on Chapter 7, provided you do not use any weapons other than the pistol. Chapter 10 is a good Chapter to attempt this as well, as your primary enemies are turrets. There are, at most, 15 to 20 Orks on the mission, and plenty of cover when dealing with the turrets.
Note: Using melee, executions, or grenades will void this achievement.
You can get this achievement fairly easily by loading the final checkpoint of Chapter 6 and finishing the mission with just your Plasma Pistol. Deal with any Nobz you find by overcharging the Pistol when you see them. Remember to complete the objectives as fast as possible or else you will be dealiing with unlimited enemies.