223 with any quality bullet at 600m is too much fun. No problem for you to get out that far with 55gr bullets. I would lean towards the Hrn Zmax simply cause they are the best value in an accurate bullet with decent BC.
Will wind bounce you around? of course but that is part of the fun.... and how you actually learn to read the wind.
Better loading methods will be needed to keep vertical dispersion as low as possible but beyond that, all the basics you use for ANY chamber/bullet apply. And what you learn here WILL make you a better shooter when you get a larger option.
We have taken the 55gr SP flat base out to 1000yds ... yeah, falling out of the sky is a pretty good description BUT it made the trip and a large pizza box target was in very big trouble.
For perspective, shooters are accurately shooting the 22LR beyond 300m... the 223 is a hot rod by comparison.
Work up your loads at 200yds for best accuracy and lowest vertical... dial up and send it... not a big deal ... really!
have fun and when you get bored at 600m.. and you will, keep going until you get out as far as your scope and reticle elevation will go.
It will be much further then your currently think remotely possible.
I have had alot of fun plinking with shooters using very large cals ... the look on a shooter with a 338/250gr option having to keep up with a 223/80gr is more fun then you can imagine... especially when you get out to 1400yds.
Enjoy...
Jerry
