Ranged Martial Disarm

[GrooveD70]

I have a question about a Zen Riflery manuever in the UMA pg 74.

Im assuming that the Ranged Disarm's SE is shooting a weapon out of someones hand. The DMG/Effect is Disarm. +15 STR to roll. On an unarmed Disarm it would add to the Characters STR, but If you are shooting a firearm what would you add the +15 to?

[Steve Long]

I'm away from home so I don't have UMA with me, but I'm pretty sure it's explained in there. Basically, you convert the DCs of the attack to STR.