I took a look at the models, and while there is some resemblance, I'd call all of them composites of contemporary firearms designs rather than being based specific models. The shotgun is the closest to resembling a real firearm, the Franchi SPAS12, but even it has some significant deviations from the real firearm. If you're interested in a pretty neat sci-fi video game weapon that is nearly identical to a real world firearm, compare the Styer AMR prototypes to the model for the APFSDS sniper rifle from the first HALO game, the form and and function align nearly perfectly.
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“The totally convinced and the totally stupid have too much in common for the resemblance to be accidental.”
-- Robert Anton Wilson