I start with Rifle twist (1-14 twist) So I know I want a light bullet in .223 caliber, I come up with 40-50gr bullets through reading. I then go to Feet Per Second ex. 3300 - 3400fps is what range I want to shoot in. So I grab a reloading manual and simply find those ranges, I look each one up until I find a powder/bullet combo that gives me the fps I'm looking for ex. 26gr of H335 gives me about 3400fps with a 50gr bullet. I will then load that load at + and - .5gr and see which works best and then maybe take the best and go + or & .2gr to find the best load, I haven't had to go to the + & - .2gr yet, but it's comming.
Here are some examples links to a .pdf that should help
5 Shot Groups at 100yrds:
Cooper Load data
AR-15 Load data
Note: I don't believe in the ladder test, it's completely pointless, maybe if you shot 3 bullets of each to see what bullet/powder combo groups the best, after all thats what we are after, this one bullet crap isn't going to do anything but waste more money...