The only thing I've ever run 1/2 grain on for load guassing is .300 Win Mag and .338 Lapua Mag. Just bacuase the case volume is so high. 70+ on the Win Mag and 90+ on the .338 LM.
Everything else is guess work, because you'll miss something, somewhere. For Large Frame ARs, I run 0.3 apart until I find something, then step that down. For Small Frame ARs, I always run 0.2gr apart. Until I find something. There's only 2 loads in my life that I ever started 0.1gr apart, and that was my 5.56 75gr Mk262-beaters, and the newest 6 ARC 108gr load.
I think you're way off, starting out 0.5gr apart - there's too much that you can miss, that far apart.