Hi,
What you're gonna learn is "simple" is really pretty complicated when it comes to recipe data.
I'll try not to be typically long winded:
The factories load "custom" powder blends we can't get as consumers, even if they're based on those we can get. They buy their stuff by the carload, test, possibly blend, and develop their loads so they attain a given ballistic performance level. Each lot's different as to the blend and charge, but the ballistics are consistent.
As consumers, we get powders blended so they vary as little as practical from lot to lot. We don't have the big labs to test stuff, so the mfrs help keep us "out of trouble" by minimizing the variables.
Best way to "duplicate" factory ammo involves a chronograph and YOUR gun. Get your favorite factory load, and run a few (5-10 is usually satisfactory) and record the results. Get the average velocity and use it as a starting point. At this point you've got $100 or so invested in a basic chrono, plus whatever the ammo cost you...
Now, look thru your loading manuals (you want as many as you can get your hands on if possible, but start w/ two or three at the least) and look for loads that duplicate what your factory velocity produced.
You'll find looking thru the books that SOME loads show up in most of them--maybe a couple of tenths of a grain different, or w/ different brass or powder. When you see that occur, it's an indication this is probably a "good" load for most everybody. It's NOT an indication of what a particular gun will do w/ it! So don't be surprised if Load A says "1200 fps" but you get 1125 on average from one gun. Next gun you test might turn in 1225!
Load a couple of the recipes up, get out the chrono and YOUR gun again, and go test...
It's a process!
Once you've been able to MATCH the factory velocity and accuracy levels in YOUR gun (I keep saying that cuz each one's gonna behave differently), then you can work toward making "better" ammo as you define it for yourself: faster, slower, more accurate, cheaper, whatever...
There's lots more to it, but I promised not to babble too much...
Rick c