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.
Kevin Thomas
Lapua USA