Proficiency: Gun

So, I've been browsing stuff in DLTCEP looking for fun stuff to change, and I entered Carsomyr (SW2H10). Since I didn't know how doing stuff on hit was done, I wanted to take a look at what's here. To my surprise, at equipping effects I found opcode 233 Stat: Proficiency. Curious why Carsomyr would mess with that I entered the details, and there...
On equip it sets the proficiency to 5.
Type 109 - Gun.

Did one of my mods (Ascencion or Weimar item upgrade) do this? If so, did this proficiency exist in the vanilla game? If it does - why? What would be the purpose of that?