desertcj,
That's a fair question but not sure anyone can give you a definate answer. A lot of reloading is trial and error and there are some things that are tried and somewhat true. For example, the .308 Win, it has been around for a while, a lot of people have had fine accuracy with it. There is a ton of information on this cartridge and what it "likes", heck there's even been factory Match grade ammo for it for quiet a few years now. You could probably get on the PA system at any gun shop and ask volunteers to come up front and give you their go to load for their .308. Undoubtedly, some will be the same or very, very close. The bugs have been worked out of this baby, but it's not 100% that all will like the same load.
Other cartridges don't have that luxury and that's where reloaders (us) come in. When I get a new rifle or cartridge, I usually have some idea what its preferred powder burn rate range is. By that I mean I know a .223 is probably not going to handle Retumbo very well. I probably can't get enough powder in the case to get the velocity I'm after. Never tried it though (hum?).
The thing that sucks, for me, is when I have my blinders on and I limit myself to one powder (or bullet) beforehand. I just know, in my mind, that this powder or component is going to be the one. If a rifle truely doesn't like that component I sometimes waste a lot of time, effort and components before the rifle changes my stubborn mind.
I have quiet a few powders on hand and do not usually buy bulk. I have never had difficulty finding the sweet spot again, especially after I have the bullet, seating depth, powder and primer all figured out already. That's me though, I'm sure everyone has a different story. I really enjoy reloading and do not mind switching bullets, powder, brass or primers if I think I can get precision, accuracy and more velocity! Then again, it's the chance you take. Good luck. JohnnyK.