You got good advice to use small base dies. The same people who never have experienced extraction problems in AR’s are always giving out the same bad advice to use standard dies in gas guns. Kick enough 223 cases out of AR15’s running the line in Highpower matches and it becomes apparent that small base sizing is a good thing.
You want your cases to be as close as possible to factory dimensions. You should always set up your dies, small base or otherwise, with cartridge headspace gages. Bump the shoulder back about 0.003 or just size to gage minimum.
This document is worth looking at. Understanding Extractor Lift in the M16 Family of Weapons http://www.dtic.mil/ndia/2003smallarms/din.ppt
If you notice the Army lubricated their cases to reduce breech friction and improve extraction. When they put a ding in the case it would not extract.
You really do not want an interference fit on your case, you want factory clearances.
Mike Venturino is a gun writer who for decades has been claiming you don’t need to use small base dies. Then, in the July 2012 Guns Magazine, he is testing a M1a and AR10 and both of the rifles are jamming with his reloads. The rounds were so tight that he could not get the bolts in battery to shoot them out and he could not manually extract them. He resorted to beating the bolts open with scrap lumber. Ha, Ha. Even Gunwriters have to eat crow at some point.
Here are some threads where people have had problems with standard based sized cases.
As for the seating die, use any, they are all good. Just don't crimp.