You must create pressure to fully form a cartridge case. The bullet traveling down the rifling has resistance, thus creating more 'pressure' to make the case fully expand to the chamber walls. Just how many threads on these interdnet forums have I read where the OP complains about his cases not being completely formed using the COW method? A 1/4" hole and a .300WSM reamer isn't gonna' work. Will the pilot fit in a 1/4" hole? #3,,, just any "rod stock" is NOT a good idea. Common 1018 is only considered 60,000# material, you'd better use 4140HT, as it's considered 70,000 material. I think a much better option would be to find a used .308 Win. barrel and rechamber it to .300WSM. It would seem to me that the fire form barrel have a shorter chamber than the barrel you are planning to use the fire formed brass in does. Lastly, ATFE doesn't care. You can spend hundreds of thousands proving in Fed court you didn't break the law or violate any regulations (which by the way, carry the 'weight' of law).