Rob,
Where's the thread posted? Hopefully not on the AWOL AR forum

I guess you get to fiddle with whichever cartridge you load, the 450/400 apparently needs filler, careful powder selection and expensive brass. The .405 is going to run a bunch of pressure to catch up but the Hornady brass is readily available and apparently very strong.

Ray's 450/416 would be right interesting, you could even leave the barrel marked "450/400" so your brass matched and not be in danger of anything but rotten accuracy if someone put the original factory load in by accident. Bullets would surely be easier to come by in .416" flavor.

Rick