I hate lost brass, especially if its a hard to get case. I do a fair amount of coyote hunting with the ar in 223 and still am a little pissy when I can't find all of my brass out in the field. My only suggestion would be to use a cartridge that has a fairly common parent case. I've had two 6mmx45 ar15's and have been happy with both of them, but I'd hardly call them gee whiz. My first one back in the 80's was supposed to be a 6mm ppc, but somehow between the dealer and the supplier it turned out to be the 6x45.