Re: New AR Biuld
About 24.0 to 24.5 grains of Varget or RL15 with a 77 is pretty much THE standard load for NM competive shooters, and should work well in your 24" bbl as well. For a bit better velocity you might want to try either N140 or N540. You should be able to bump those up by a grain or so for the 69s. For the 55s, I'd recommend a faster powder, something like Benchmark, H322, N133 or even N135.
Easy combination to load for, since most everything seems to shoot in this one. Full length size, use a chamber gage to set up initially, and avoid crimping (neck tension alone is sufficient, if it's down around .002"), and they should do just fine for you.