It all depends on how you want to prep your cases. Every die company has the basic 2 die set for bottle neck rifle cases. Most straight walled cases are offered in 3 die sets. A full length sizer and a bullet seater dies are included for bottle necked cases. Most companies include a crimping feature in the bullet seating dies so you can crimp or not, depending on how you set the die. This is all you need for basic reloading of a bottle necked case. Most offer 3 die sets as well. The third die does different things depending on the company. In straight walled cases the third die usually flares the mouth of the case so lead/cast bullets seat with out shaving lead off of the bullet base and side. Basic die sets will get the job done. If you really want to get fancy with your reloading then there are all kinds of options, like neck sizing dies, neck collet dies, bushing dies for sizing, for neck sizing, bullet seating, etc. I tend to get by with good basic sets for my straight walled cases and get a little more exotic for bottle necked cases. I just bought a set of basic Hornady dies for a new 7-08, but I added a Lee collet die to size the necks with. Depending on how heavy I get into it, I may add bushing type dies later; but the set I got to start with will do every thing I need. Bottom line - the third die you speak of is for loading lead bullets. If you are not going to load lead and only jacketed, get the 2 die set. If you are going to load lead or think you will load lead bullets, get the three die set. Good Luck and Good Shooting