An interesting idea, and very cool if true... though consider me (for the moment) mildly skeptical absent further evidence.
First to clarify timing, while the above Leatherworker post was published in 2012, the period it seems to reference would have to be 2005/2006, as Joss Whedon departed
Wonder Woman in very early 2007. He certainly had a
Serenity sequel of some form in mind, but all of his public statements were pretty wishful, and I'm not aware of any solid confirmation of serious studio interest at the time (either Universal for a film continuation or Fox for a TV series resurrection) beyond essentially vague rumor. [Anyone by all means correct if I'm wrong.]
The maker attribution is at least accurate; Ugo Serrano (who apparently worked on
Firefly and/or
Serenity space helmets via Global Effects) posted a photo of the same pistol build unholstered on his Instagram
in 2017 and
in 2021, albeit without specific mention of a pre-production context:
The 2017 caption was edited in 2021 to be identical to the new post, so it doesn't lend anything additional apart from a reply to a query as to whether both were his work: "
no just the top one the bottom one is a prop from the show the client borrowed."
Note that the build reference is
Firefly-style, rather than
Serenity-style, yet the build incorporates a clearly
Serenity-reminiscent magazine. Considering that Joss was still cooperating with Universal at this point, with the Collector's Edition DVD released in late 2007, I would expect a Joss-involved project to have been with Universal. Why not a
Serenity-style reference, then? Plus, while a sequel story was eventually released in 2014 in the form of a comic book
Leaves on the Wind, its writing was principally credited to Joss's brother Zack, suggesting Joss never got all that far along.
So it's not impossible this was an original prototype, and I'd love to see corroboration, but it strikes me as surprising that development would have reached the props stage. If I had to bet at present, I'd say this makes more sense as a fun private commission.