OK I figured it out. I have to switch the inner piece also, not just the rubber ring.
OK, I'm an idiot. I have a Topeak Turbo Morph G frame pump. I bought it awhile ago and lost the manual.
Now I want to learn how to inflate a Presta tube with this pump before I hit the road, just in case I need pump up a tube. But for the life of me, I can't figure how to switch the head to accept the Presta Valve.
http://www.topeak.com/products/Mini-Pumps/TurboMorphG