I have been trying to get passed round 9 on this challenge and I think it's almost impossible, unless you get lucky with the box and it gives you the right weapons the first time. Your going to need luck and skill for this one. Check out this challenge,
please let me know how far you get, cause its just one of those challenges.
there is maybe one shotgun i believe which is the s12 even with double tap its useless after 18 so...
If I didn't read your post and just read your title. I would have gone out of my way to get you past round 9. (you dont see that much from me), lol.
The challenge seems easy enough, I once went to round 26 on Nuketown using the Hades (upgrading base shotgun) and that automatic shotgun.
But I haven't tried to do this on Tranzit,