This achievement can be earned on the Outlaw to the End downloadable cooperative mission in Read Dead Redemption. To get the Dodge This achievement, start a private match with a friend on the Herd mission. Once the mission starts, select the bolt action rifle and the rolling black rifle. Use the bolt action as your primary weapon, and shoot the TNT crate next to the tent on the righthand side. Quickly switch over to your rolling black rifle. Have your teammate use one of the repeaters to weaken the stronger enemies, then start killing enemies.
The larger enemies will take two shots, whereas the slimmer ones will take a slimmer chest shot. If you just start off using the sniper rifle, you won't have enough bullets to kill ten enemies in a row.