This Scar is something I've put hundreds of hours into, the usual difficulty is the near complete lack of reference for internals, I do have many pictures but not many at useful angles. It may seem very strange that I model all of the internals, but for my own personal projects it has many uses, and once complete I can build limitless low poly meshes and perform bakes from it, though I've been working on a physical weapon system in UE4 for part of my main project, all of the internals will be functional in the final, at the time of writing this, I am currently modeling the bolt, but it's very complex with all of the internals, the process and math is something I'm still planning out.
I've put up 2 sketchfab previews, one is to show how the normals baked, there are very minor errors , the other is just a really cruddy texture to get some idea of how it'd look, the triangulation hasn't really been touched a great deal, especially on the round areas, but I will clean them on the final.
Lowpoly Bolt Carrier Normals preview
Bolt Carrier Textures preview - Sketchfab compressed textures :c