Gotta go with those above. Creedmore is hornady's baby and brass is pretty readily available. I have shot a lot of .243, but you don't see many .243 uppers being built because of the longer case. 6cm is gaining steam as a great mag fed, repeater compatible short action cartridge. That means it can accept the long bullets and still fit in a stander short action, along with feed well out of a magazine. I looked into 6.5 cm pretty hard, but just couldn't bring myself to jump on a case where Hornady is the leading producer of brass. I do not know much about forming brass from .308 or .243, but it seems pretty labor intensive with the long neck and sharp shoulder. It's not a simple size and trim.