Here's an idea I've been pondering. What if someone took a 308 and necked it up to 44 cal for use in an AR-10? I think that would be a pretty sweet little set up. It would be a great round to cast for, the brass is cheap as dirt, and it would be a good deer rifle too.
I'm not sure how to make that a reality though. I know you would need to order a custom reamer and possibly custom dies. I'm not sure how you would go about actually designing the cartridge and developing load data though. Any ideas what kind of velocity you could expect out of this with 240gr and 310gr bullets?