I load both 40 and 45. You need both conversion kits (one should come with the machine if you are ordering it from Dillon). If you are ordering a 650 from Dillon and they set it up for one caliber, get a 650 quick change kit for the other caliber. It will include a stand to hold the toolhead for the caliber that you do not have on the machine. Get the casefeeder. I am not sure if one plate works for both, I have both pistol plates. Get two powder checks, or buy 3 at a discount. As far as the priming system goes, all I can say is make sure you have loaded a lot of the caliber you have on the machine before you switch the machine over to loading the other caliber. Not that it's a problem doing it, but the time it does take you could have loaded a lot of ammo!! You will also need a scale, caliper, etc, etc. if you are just starting to reload. Hope you enjoy your machine, the only thing I find more enjoyable than using mine is spending time on the range!