Actually the small base die is also a full length sizer die. The difference between a small base and regular full length sizer die is that the small base die sizes the base of the cartridge case more than the regular die. How much more depends on the cartridge for which the die is made. Yes, the small base die does work the brass more and can lead to shortened brass life. I would start with a regular full length sizer die and only use a small base sizer die if it is really necessary. I only own one small base die. That is for my match chambered .308 bolt gun. I have to use it on cases that are once fired in another chamber (i.e. Lake City Match or M118 brass). New brass does not require a small base die to fit and once the brass is fired in rifle I can use a neck sizer die from then on. But that is a bolt gun. A semi-auto would require a regular full length die. I don't use small base dies for my Garands (I have 9) or my ARs (I have a COLT HBAR and a RRA NM). I can use the brass fired in either AR by running it through my RCBS regular full length sizer die. I can do the same thing with my Garands. Two of my Garands have tighter commercial chambers while the others have USGI chambers.