First of all, 2 of the achievements i really dont know how i got them but they poped up so i will tell you what exactly did.

I got this one by starting the game. If not you should try to join a server(when i did was imposible cause nobody was playing) or create one.

This is so easy! Create a server and before you respawn there is a buttom at your left what says Customize and where you can change your weapon and the skin.

In my first try i created a server in train station map, selected a weapon with vulcan skin and then run at the right over the tunnel following the rails (The game crashed) so closed and started it once again doing the same but when i spawn i just start to run over the map.
My first step was go throw the stars in front of you (I couldnt go further so i was shooting there a little bit) then went back and go to other stairs that you see at your right when you go downstairs. At this point you go upstairs and you will see some kind of bridge that you should try to jump at the top(You cant cause of textures and when you fall should get the achievement, at least i did like that). Next screenshot shows the bridge i mean and the stairs are at the right.



I was so confused about how i got the bomber achievement (cause looks like you have to plant a bomb or defuse it to get the achievement, and not this randomness) i kept exploring the map and when i went upstairs of the last place to visit of this map this achivement poped up. The next screenshot shows where exaclty got it but i really dont know how and why.

I really dont have a good argument to explain how this works but i think its more about explore the map and run over it than do one thing in particular.

If you have some feedback about how you got it post it here to share with other players.

Hope this can help somebody!!!