xj,
You need to read a book on loading. A good one to start with is the Speer Manual #13. The beginning of the book is very educational. Last part of the book contains loading data which you would use if and when you load your own ammo.
Or you can go to your local public library and check out "The ABCs of Loading" which is somewhat informative, but not worth owning.
Also check the web for bullet companies — there are many of them. They often have lots of info about their products.