What I do is a lot like Baylor243 wrote in post #16: shoot the rifle/factory rounds using a chronograph, note the case used, measure the rounds for headspace, COAL, CBTO, pull the bullets on 5 factory rounds, measure the powder charge on each pulled round, then measure/weigh cartridge case water capacity, make note as close as you can as to the brand/designation of the primer used. (not too hard to figure Federal brand ammo would use Federal brand primers), and of course the brand, type/style, weight of the bullet.
I then set all that up in QuickLoad for the caliber used (you can use whatever computer ballistics program you favor). Then I select the powder(s) using the charge weight/average weight of the pulled rounds till I find the one(s) that meet the velocity/average velocity I have recorded when firing, BUT showing a safe pressure in the program (I don't have any means to determine pressure when firing other than inspection and computer estimation).
Then I look through the reloading manuals in my stack (don't have 'em all) to compare.
Lately, after following Muddyboots on crimping with the Lee Factory Crimp, using calipers, I measure the crimp on a factory loaded round and apply this to my handloads.
When I started all this "Homework", the price of gas was as now or higher. Saved trips to the range.