what parts and work are needed to change a 5.56 ar-15 to a 6.8 spc? do I need a whole new upper, or do I just need a new barrel, bolt, and magazine? is this something an amature can do? also, when building the original 5.56, after it iis assembled, what is involved, if anything, in headspacing it? I admit, I am not 100% sure what this process includes, I have just heard people talking about doing it. is it necessary in the ar-15, I typically hear about doing it in bolt/lever actions. thanks for putting up with the "dumb" questions! have a good'un!- Travis