I came across a story of a guy who worked for the military back when the .408 was being developed for their snipers, and apparently he loved the .338 caliber so he necked the 408 down and experimented. If I remember correctly, he lost all accuracy after 300 or 400 rounds. But he loved it while it lasted!
Yes, a Mc will work. My gunsmith has been building .408 chey Improved's on Armalite AR30 actions for some time now. It seems to work well according to him.
Barnes is currently and somewhat hush-hushidly <font color="green"> turning </font> bullets for this caliber on a lathe like LRBT is doing. Bad news is that they cost the same, just over a buck a bullet!
I can't remember exactly what my gunsmith said he is using, but it seems like it was 175 grains of powder or thereabouts.