I load my test loads for .204 and .223 in .1gr increments due to the small case size and start a full grain below published max load from a couple of sources...Usually the bullet and powder manufactures respectively...
I put together 10 rounds of each charge weight and only fire five until I get the best group from a really stable firearm set up, using a lead sled, where all I'm touching is the trigger...Once I find the best accuracy, I'll use the other five rounds as verification for the load and tear down the others to reset the components...
I run magnum primers in both of my .204s, CZ and AR..Using 39gr SBKs, I get the same degree of accuracy out of both rifles with the same load...
The load below was worked up in 2007 and I've never found a reason to change it...Most of my really acurate loads will fall between .4gr and .7gr below published max..
This is a couple of good loads that came up for a .223
Obviously, only change one component/factor at a time when working up test loads...If, for some reason, I don't get an acceptable group at first, then I'll start working with seating depth in very small increments, but usually that's the last factor I consider...
This is my set up for using a lead sled,,,The sled is strapped to the concrete bench and the rifle is lightly strapped to the sled to keep it from moving once I get my sight picture...