The BP is basically a MG47ES with out a butt stock and the pistol grip mounted under the barrel. The receiver is a shortened MG47ES and the bolt carrier, and FCG is from the extra parts I made for the ES tutorial that's why it is heavier than necessary. It could be made with 1/16 rather than 1/8 receiver material and save a lot of weight. There is only a few real differences. For details, just ask and I will take some better pictures.