New build / a Stag lower with a DPMS upper .223-1/8-24 inch SS barrel now need to find some load's for it with 55 gr. MK, 68/69 MK and 77 gr. MK am i trying for too much and does anyone have some loads i can try.
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.
I use 24.5gr of Ramshot TAC, with 55gr bullets loaded to 2.260" for my AR. My dad uses 25gr of H335 with 55gr bullets in all of his AR15's and bolt guns, I want to say he loads to 2.255". CCI 400 primers for both in any brass we can get. I shot some 75gr A-max with TAC powder and it did very well in my light weight AR.
H322 works well also with 55gr bullets, 23.0grs worth.