Is there any way to make fail percentage making weapon with xml?

[tobe]

I'm planing to make reinforce weapon mod.
Like surgery, I want to make fail percentage to crafting weapon.
And I think I can make it from copying surgery code.
But I can't find relate code in def_surgery.
Please help me find it! 

[Karthas077]

You're not going to be able to do this with just defs. You'd need to write a custom bill class in C#.