My "Infallible" is selective, chosen by a thumb slide set into the left side of the top tang. It is however not "Re-Setting", ie unless altered by moving the slide it fires the bbls alteranately, regardless of whether the gun may or may not have been opened & reloaded between shots. Thus if you fire the right bbl only, open & reload, the next time you pull the trigger it will fire the left, unless you reset the slide to R. The setting slide itself moves to other setting with each trigger pull.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra