I was just messing around online yesterday and found the 6x45 round (.223 necked up to a 6mm). I was just wondering if anyone has one of these in an AR? Sounds like you'd just have to rebarrel it and everything else would be the same. Just looking to improve on the .223 without having to spend a bunch of $$$ to change out the whole upper. How much of a difference in drop is there with both shooting 75gr bullets? I was thinking of this round for p-dogs out to 500-600 yards, but mainly within 300. Thanks for the info!