AA2015 and R10x are my go to 223 powder for 55 and down. I also love N133 but it was too cost restrictive to get too excited about. I believe the Canadian made AA2015 is just as good and meters better. It is possible that R10x (the recent stuff) is just as good also and the three for me have been basically interchangeable in my 223 loads. I fireform 223 Ackley (60 freebore standard Ackley reamer) with 25 grains of N133. AA2015, or R10x. All will shoot, without exaggeration, zero or .1 groups at 100 in my 14 twist Krieger and the shoulder will be nice and sharp. I use Lapua, LC. amd WCC brass. My absolute favorite bullet in the 53 Berger or the 52 Fowler. I just bought 16 lbs of LT-32 at the urging of Bart, I think it is slightly faster. Should be excellent for 40 grainers for hopefully over 4000 fps in the Ackley.