For sidearm I guess an M1911 45 ACP semi-auto handgun would fit him, if with 21st century stuff to upgrade M1911A1 versions could be with underside rail and suppressor like the MEU(SOC) pistol variant.
Vid from Garand Thumb shooting this 106 y/o M1911 that's WAY more advance & much better alternate option than Orthax's trashy deal to make the first firearms such as the The List- https://www.youtube.com/watch?v=j1smiOWim2o
Similar to Templin Institute's The World of Tyrrell | Low Fantasy Setting https://www.youtube.com/watch?v=-jbGeLk7DgU&t=711s
As in US's Central Intelligence Agency's division Special Activities Center to deal with problems from Exandria (Sometime in the Post-Divergence era but a couple years before Vox Machina was founded) more clandestinely + covertly by sending its black ops paramilitary force consists of agents, operators & contractors to even maybe assists said 3 adventuring parties Vox Machina, Mighty Nein & Bells Hells to would give the US some advantages in the new world with benefiting America's interests I guess. Cool?
Also various types of firearms with gunpowder based weaponry provided by the CIA be used by various characters from each of the 3 parties (different timelines) for different range engagements against different foes. I'm sure Percy from Vox Machina would be VERY glad in joy to try out better quality firearms (similar to this scene Stargate SG-1: S05E18. The Warrior shows the FN P90 PDW's effectiveness that shows this is a weapon of war) than the DIY pepperbox revolver "The List" he made when made that trashy deal with Orthax.
Inspired by these 2 videos-> https://www.youtube.com/watch?v=vuxsRox7okg
https://www.youtube.com/watch?v=c4Rt8nxhMA8
Thoughts @NextScorsese? Take ya time to respond my friend.