For us that don't have any friends the achievement deadeye is a pain to get, but their is one easy way to get them.
The Easy Way
Somethingthat I learned while trying for the achievements is that the achievement counts even if you headshot your allies.
The easiest way I found when alone to get any deadeye achievement is by doing the following:
- Join a empty entrenchment co-op server through the server browser.
- Wait for the bots to get into their stationary defence postion.
- Headshot your allies until their is one left and let him go and regroup.
- Once they regroup you have another wave of easy to hit bots.
Something that I also noticed was that if you are going for the meele achievements this guide also works for them too, but you must wait until the end of the round for the achievement to add on the amount of kills you have to your score.