Status update: I un-spaghettied the movement code a bit. As I suspected, the differences in movement between weapons is encoded in the copy-pasted movement code, and I haven't adjusted for this yet, so right now everything handles as if it's the pistol. I'll poke at it a bit more. I could probably zscript-ify a lot of it, make it easier to alter the movement properties.
[EDIT]: Also, I tried putting together an upgrade item for the handgun. Since you suggested replacing the handgun entirely with the SMG, I figured, why not just make the "SMG" a full-auto conversion kit for the handgun? It fires every 2 tics, which is slightly faster than the AR (which fires every 3 tics). I might try upping the mag size as well later, but right now it feels pretty good.