Sig p320, looks to be the M17/M18 version with a manual safety, not the extended 21rnd mag though, probably the 17rnd mag; unless CA, NJ, CT, IL, NY, MA, WA, (fuck I know I’m missing one or two), who restrict their citizens to 10rnds arbitrarily. That’s a double stack 9mm magazine, def more than 7rnds.
In theory it could be a .40sw, but afaik they don’t make them in that caliber and you’d need at least to rebarrel it if not need a new slide too, and new mags and such ofc. That isn’t impossible, because they do make those parts for the regular p320, but afaik they only make the 9mm version of the slide with the manual safety, more likely that it is stock.
You’re right though, the more rnds the better, but also concealability is a factor. Tbh, we don’t know if he has an AR with 100 surefire 60s stacked up right off camera, either, but we know that wouldn’t fit in his pants lol.