223 at 600 yards and beyond will just nock the paint off a 1/4" mild steel target just as info so a larger target is cheap. 4" at 600 yards very tough with variable winds forget it. If you can see your trace or misses on a calm day maybe. Go heavy with your bullets. Krieger can't go wrong but WOA are very good also. I have both. Go with a heavy wall upper Vltor MUR, MEGA Arms SBU or DPMS thick walled slick side. 1-8 twist or 1-7. I prefer 223 rem chamber but 223 Wylde is very good and better selection of barrels. Wind will play with you bad with 223 at 600yards. I run a 20" 1-8 twist barrel for the velocity 24" would be better and out to 600 75gr hornady match bullets work ok and there cheap. Past 600 yards I like the 75gr or 80gr Amax bullets they will stay stable threw the stransonic stage of flight. I've taken mine out to 885 yards it is very tough at those ranges with a 223. I build a 6.5 Creedmoor chambered large frame AR and it is way way more fun at those ranges. But 223 can get you to 600 yards with 223 I've shot a few 2.5" five shot groups at 400 yards but I would not say that is the norm it is a lot of fun seeing just what the caliber is capable of