Whenever I get a new BCG I take it apart, oil it up good, re-assemble and then use my fingers to run the bolt in and out a whole bunch of times to wear it in a bit. You can do this while watching tv.
While doing this I also add a few drops of oil into the two tiny holes on the side of the bolt carrier that will lubricate the gas rings. New BCG's with new rings just do not slide in and out of the bolt carrier easily until broken in. You can tell the difference as the parts wear together a bit to where the bolt rotates and slides in and out the bolt carrier easier with finger pressure. I had a new BCG one time that was so tight I could not pull it apart by hand. If you do not want to go to all this trouble manually run a bunch of sonics through the rifle with the BCG oiled up well.