If the rounds aren't going into the barrel chamber without resistance, just under the force of gravity (with barrel removed from slide), it would seem likely that either some of the rounds weren't sized as well as the "gauge" might think, or else you've got something stuck to the chamber wall?
Also, in an occasional older 3rd gen we used to take a "finishing" chamber reamer to lightly clean up any high spots in the chamber. This sometimes revealed high spots, too. We cleaned up a few "tight" chambers that way. Obviously, this isn't something that someone ought to attempt without some understanding of how to properly do it so damage isn't done to the chamber shoulders & barrel leade. Barrels aren't inexpensive.
