If Marksmanship Rating is B, COR/DD is a very viable DD/Support function.
Marksman Belt that adds +5 to the MM skill
Merit caps at 16 skill.
Torque that adds 7 skill
Total of +28 possible MM Skill
Maximal outcome @ 75 would be:
B+ 256 + 28 = 284 (RNG with capped merit on MM skill)
B 250 + 28 = 278 (A+ rating)
B- 240 + 28 = 268 (A- rating)
B+ 256 + 23 = 279 (RNG with 5 merit on MM skill)
B 250 + 23 = 273 (A+ rating @ about 74)
B- 240 + 23 = 263 (A- rating @ about 74)
For RNG the capped MM skill would be 269 + 28 = 292.
So COR/RNG or COR/DD could seriously mimic the DMG outcome for RNG; but as far as the weapon selections, COR are limited. I saw that the best gun/bullet combo would be: Corsair gun and iron bullet which came out a little under 100.
However, I believe that the Phantom Roll ability would put the DMG outcome on par with RNG. I haven't tested it out yet but it does look promising from the Roll list.