I have a client with a similar problem. I don't know if this will work exactly for you. They purchase metal in pounds but stock it in feet. The issue is that every shape of metal extrusion has a different weight per foot. We created a different UOM Schedule for each shape and each shape was given a specific part number.
Now we did not consider the length of the pieces. If we received 1000 pounds and it converted to 1275 feet we took that into inventory. Some pieces are 8 feet and some are 8 feet, 3 inches. We expect a loss of a specific percentage. In manufacturing this loss percentage can be calculated into the scrap factors. If you are a pure distribution shop then the only way to account for drop (the short ends left over by cutting pieces) is to perform a scrap issue transaction every-time something is thrown away.
Hope this helps