Scrap Management in Sub Contracting(Bug Not Working)

Dear All,

We are fabric manufacturing unit , we are struggling with new kind of issue , When a fabric is sent for dye some fabric comes as B-Grade that is scrap but it is sold.
I have created BOMs and added Scrap in that but when I am adding Scrap in Purchase Receipt it is showing me no effect , I am adding scrap of 370 Meters in Purchase receipt but it is not deducting it from the raw material.
any solution? The only solution i can think of is to add a new BOM for B-Grade and Consume it but it will seriously affect costing

So you buy scrap, or proccess scrap?