If you can't find load data for the .243 Winchester and 100 grain bullets you aren't looking very hard. And no, it doesn't have to be brand specific either. Load data for the 100 gr. Sierra, Speer, Nosler, or Hornady works just fine for the Core-Lokt too. And this " 42 4350" is poor advice, there are different "4350's" and a grain or two can make a difference as they have different burn rates. Also, is this a beginning load or a max load? While I know that is a max load or near max load depending upon the type of "4350" just throwing that out there without the details leaves a beginner with some potentially dangerous choices. IMR-4350 or H4350 is my first choice for the 100 gr. bullet weight in the .243 Winchester but the data will be slightly different. A really well researched web search and/or a reliable loading manual is in order here.