First Mission Obtained: Rail Line
This achievement requires you to get all 15 kills within one ammo clip. You can upgrade this a little if you want to for help, but it should not be a problem. The best place early on is when you must chase after Kathryn who was abducted by the enemy. You will face a lot of enemies here, and it's a very straight forward path. You can switch weapons and use powers at any time as long as you don't reload, so when you must kill the heavily armored troops, use somethin else to kill them.