I would say move whatever we have to dedicated fan wikis. The Auto-9 stuff for example can be moved to the Robocop wiki (if they need it).
A few more comments:
First thing I'm 100% sure about is that we need to have a category for concept firearms, including the likes of Saritch, MR-C, and Sterling Bullpup. These are weapons that were never properly made into prototypes (thus they don't fit the Prototypes category) and exist only as concept or mockup.
What differentiates them from fictional firearms however is their intent and notability. We're not documenting Halo's sniper rifle or John Doe's pimp my gun concept rifle. Inclusion I think should be modeled after Wikipedia's notability guidelines, but more open on firearms and focused on them. Wikipedia wouldn't document some of the stuff we document here because we're more in depth on the whole thing. I would say MR-C just barely passed the threshold of non-fictional intent (its one page on the official website points to that at least "somebody" at Crye Associates isn't treating it as a Ghost Recon fictional gun) and notability, but needs a lot more context on the Ghost Recon discussion.