Modern AR-15 style service rifles fit a pattern based on the rules of the game. As such, they have a particular 20" barrel profile and most competitors will shoot both magazine length at 200 and 300, and then single feed (too long for the magazine) at 600.
Service Rifle loads tend to become Pet Loads that use match bullets and favorite powders. The chambers on popular rifles like WOA and CLE, are a hybrid design of a Wylde Chamber. They can take full 5.56 NATO pressure loads and ammo, where that isn't recommended for 223 REM.
Of course there is always a pressure overlap between those two (5.56 and 223) when the twist is common. Most Service Rifles will run twist at 8 or faster with 7 being common. This allows using 69 - 77 grain bullets at magazine length, and then switching to ones like SMK 80 or similar for the 600 yard line. BTW, many SR loads are hard on brass to the point where four cycles usually retires the case.