"... for a more civilized age."
Kill 10 enemies in a Firefight or Campaign session with the DMR.
This achievement, like many others in Reach, must be done on NORMAL or harder difficulty settings. Luckily, that is a minor hurdle.
Also, this likely needs to be accomplished in one life if attempting in Campaign, or one map in Firefight.
The DMR is an excellent long to mid-range weapon -- it's certainly "not as clumsy or random as a blaster." One of the easier ways to accomplish this achievement is to start a Firefight session and select the Recon loadout, which gives you the DMR as your primary weapon. Headshots make quick work of the unshielded foes, so focus on grunts and the like to make this go quickly.
If you are having troubles, you may want to utilize a custom skull that grants invulnerability or higher damage to your shots. To do this, go to the firefight lobby and select game options, just above start game. Select firefight settings and at the bottom you will see custom skull settings -- here you can select the spartan traits for one of the three colored skulls. Feel free to experiment with what works best, but just remember to turn the skull on in the wave properties for each round with which you would like to have extra help.