If you send me a friend request then ill show you if you can't figure it out.
Go to the room in Kalach where the machine gun is and then go into that bathroom beside it. Go from there to that empty room then into the room that has snow in it and has two boxes in the corner.
Stand on the very edge of the box but not in between the box and the wall or you will get stuck.
Friendly fire must be turned on and you must have another person. That person is to stand in the corner infront of the box.
Now here is the part people don't get - hrow the grenade right beneath him and jump towards the board on top of the window. Then jump onto where the boards are floating in the air. Don't worry you wont fall off.
Now face the window and put your body against the wall, run and jump and keep pushing left and you should fall into the snow on the side of the level. Most of you wont understand this and it may take a few tries but if you can't get it feel fre to send me a friend request.
- SWA MrHoRtnBiA