Many very good long range shooters on this site EDGE, JMACK and RGinIdaho are a few that wouldhave very good information...
your Ar15, with the right optic and the right bullet can get out to between 750 to 900 yards , generally
Reloading quality ammo is possible on a progressive press.As Travis points out learning to shoot long range with an AR will be as much an equipment issue as a skill issue. Battle rifles are not inherently accurate although some are better than others. Some things to look at with your .223 AR, you’ll want to shoot the heavier bullets but need a fast twist barrel to stabilize them 1:7 is best but 1:8 will work, if you are starting out with a 16” barrel chances are good that to get the velocity you need you will have to load them longer than will fit in a magazine so you’ll need to single feed. Two of the biggest hurdles with an AR will be getting your setup shooting sub MOA at distance and spotting your shots out there whether you hit your target or not.If I were going to work on my long range shooting skills with an AR I would shoot for group size at 100 – 300 yards in different weather conditions and forget about trying to find the limits of the .223.