ATM we can't inject custom first-person animations into PAYDAY 2 - all we've gotten is an extremely crude method of parsing SMD animations that only safely works in menus, and even then it barely works to begin with because rotation in PAYDAY 2 is extremely wonky and a total pain in the rear to convert to. Which means that, until we either get an updated SMD parser that works in first person and takes kindly to rotations or someone leaks OVERKILL's in-house animation compiler(s), an RMB-93 is going to be impossible seeing as you pump it forward instead of backward like on a normal shotgun.

All of this being said though, the moment we get some means of modifying/replacing animations for this game I'd be more than happy to port an RMB-93. That gun saved my life more times than I would like to admit in GR: FS, and of course the level of complexity behind customization in GR: FS would take nicely to PAYDAY 2.