I made a video guide on both Full Strength and Ranger Hardcore since I think being sneaky helps through RH a lot. However, if you only care for the Hardcore achievement, ignore the optional objectives in The Caspian.
Note that this NOT a speedrun nor a seamless run, but I have done my best to edit out the parts where I failed or was too lucky in order to provide a more reliable way for you to follow. I hope that you find it useful. Please leave a like on YouTube if so and feel free to comment and ask questions if you need more help.
Chapters*
Moscow - 0:00
Winter
The Volga - 0:36:15
Spring
Yamantau - 1:48:15
The Caspian - 2:03:10
Summer
The Taiga - 3:34:20
Autumn
The Dead City - 4:21:25
* I have removed the scripted sequences/chapters and cutscenes where not relevant as you cannot die or make mistakes there. When I played, I skipped and saved time where possible. If you would like to build a relationship with your crew, listen to them and take part in the activities on The Aurora. It may help but is not required for the best ending.