I'd be looking at the 55g bullets also or 62g pulldowns (m855's). 100yd to 200yds is point blank range for a AR in 223.

A common load that seems to be an excellent starting place for load developement is 25.5g of blc-2 powder & a 55g to 62g bullet. They to use faster burning powers in your short bbl's AR, you'll get better performance. They also sell pulldown powders (military sirplus) that are cheap & flat out work in the .223's. I like the 846 better than the 844 but that's just me.

Check out gibrass, it's a great place to buy reloading components in balk.Welcome to Bartlett Reloaders - Jeff Bartlett

Another must have for your new AR is a conversion kit (22lr). These thing are a blast, easy to use & you can get in a ton of trigger time in for little $$$$.

Kep um in the black