Will any BCG do, or are some better than others? The only thing I've heard/read about any is the chrome will come off of the DPMS. Any I should steer clear of? Some have a fairly large difference in price so I'm not sure if they're selling a superior BCG, or a name. Also, how do I go about having it and my barrel/bolt headspaced? I've got a new barrel on the way but still need the BCG and I'm not very familiar with this process. Thanks.