Yep, A 223 is big enough for antelope at 300 yds, and a 22-250 will do it at 400.
Let the flaming begin!! Just going on personal experience here. They work.
But for long range shots the game changes.
I haven't found the perfect LR antelope round yet, but am looking. A 6.5 WSM seems the closest so far.
I shoot a 7 WSM right now, but haven't shot an antelope with it yet, tired of killing the things, I'll let someone else shoot'em.
This one got some .243 medicine from my wife last month.