I compete as a prone shooter out to 1000yds.
If you want to shoot Fullbore with iron sights your choices are 308 win or 223.
If you want to shoot any rifle which is a combination of iron sights and optics at 1000yds, 243 win 6.5-284 or 7 RSAUM would be good choices.
Steve Bair
I must disagree, the quality of the scope is answer.
I have a March 2 1/2 to 25 power i use in competition.
I use this scope on 2 AR platform 6 fatrat uppers and a 5.56 practice upper.
I also use it on my #2 1000 yd prone rifle, in the winter i put it on a dedicated 22 rimfire upper for indoor...