Just add a user property "splintering weapon". After that you need to add a simple rule using this new user property. When you add that simple rule, you change the logic to ">=" and add what you want the trip point to be. For example if you are looking for weapons >= 20%, then you select your "splintering weapon" property, change the logic to ">=" and put "20" in the edit box next to the logic type and press "Add". This rule will then appear in your "Rules" pane. After that just select this simple rule and make it "Active"