I was messing around with this spot and managed to clip through the mountain side and I can see completely under the map but sadly got stuck. I am going to keep working at it since it might just lead to under the map.
Edit - Well I just fell under the map and died, I am not sue if there is a death zone under or not but at least I know now that you can get under that way so now it's trying to see if I can stay alive under the map.
I find bayonet jumping pointless, you would never be able to do it in a regular game, unless you have a friend on the oposing team, but yeah, it's kind of useless to have bayonet jumps.