We have two types of attributes for this. "Weight", which compiles to weight of Advance Steel objects without taking in considerations copes, holes or cut backs. We also have the attribute "Exact Weight" which takes into consideration copes, holes or cut backs. Simply change the attributes in your BOM templates or the templates editor depending on which type, "old" or "new" you are using. You can check which ones you are using by going into your Management tools, defaults, in filter type "bom" and in the Drawing-General section if you are using new or old. You should use the new BOMs... (Therefore the second line should be selected.)
You can modify your BOM templates at : C/ProgramData/Autodesk/AdvanceSteel2015.1/Shared/Support/BOMTemplate.