wncchester, I know you the the rest mean well, and you are right most of the time, but there are some AR's (and not custom target chambers) that flat do need small base dies. Most do not...at least not in non combat scenarios.
I've owned several semi-autos that don't. But back Obama November, I bought a Remington R25. That's a DPMS-built, camouflaged AR-10 style, .308 chambered, semi-auto. Accurate as hell, but chambered really tight.
Factory Remington fodder can be shot as fast as you can pull the trigger, with no trace of misfeeds or other problems. Cheap blue box Federal fodder, only chambered the first round, then refused to feed the second round. Russian "Wolf" cheap stuff wouldn't even chamber the first round. Bolt would not close. My reloads that were carefully sized and shoulder bumped, slid right into my Wilson gauge. Unfortunately, they chambered about like the Federals. I called DPMS.....they said get an RCBS small base sizer and the problems will disappear.....they did.
Oh, and by the way, the bases are sized only .002", only .001" more than my regular sizer. That's not enough to worry about. Ejector damage from the Rifle will be the limiting factor for brass life, not sizing a miniscule .002". Shoulder bumping is way more damaging, so don't over do that.
You may never need a small-base die, by all means, buy a regular sizer, first. If that doesn't cut it, you will find a small-base sizer to be a God-send! Don't make the mistake of thinking that RCBS is stupid. They've been in this business longer than any other major reloading company.
One more thing. If you ever think you want to hoard AR ammo away for SHTF tomorrow, do yourself a favor and buy one of RCBS's new AR sets. They come with small-base sizers, and can guarantee that they will feed flawlessly in any AR. In that scenario, who cares whether you get 5 loads out of a case or 8....you will probably not even be able to pick up the brass anyway, running from zombies!
