The one weapon mod on marksman mode makes it fun and challenging, until you get something like an earthquake or rampage. I'm sure other people have said this before, but I think that weapons not compatible with the marksman mode should be impossible to have in your arsenal when playing in marksman.
Kyle already did the same with rebound but you know it was too hard make it also for marksmann.........Look the positive thing you have a bunch of new songs that you would probably never use in all your life time!