The longest barrel I reload .223 for is 24" 1:12. I've had very good luck with the 55gr V-Max and Varget powder. I've heard a few posts on here say there are some newer powders that burn cleaner than Varget, but that's hard for me to wrap my brain around. I'll have to try some one of these days to find out for myself, but Varget has been a very clean and consistent powder for both my bolt actions and AR's.
Rednecks... Keeping the woods critter-free since March 2, 1836. (TX Independence Day)
I'm going to use the words "clip" and "Long Colt" every chance I get. It grinds my gears to see new members attacked when we all know dang good and well what's being refered to.