There is apx 200fps difference between an AI and the 6.8 based cat.
http://www.6mmbr.com/223rem.HTML

This version was first chambered in 2007. It's is a simple neck down using 6.8 bushing dies but the case is trimmed 1mm shorter than a 6.8 so the 75 and 80gr Amaxs can be shot from the mag at 2.295.
I've used everything from 10X to RE17 with 75Amaxs and been able to get 1/2" or under groups. I shot 1 group of 5 at 100yds that measured .151", several .2-.3 5 shot groups.

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