I HAVE EXPERIENCED 3 STOPPAGES OUT OF 50 RDS. RECENTLY IN BRAND NEW TAURUS PT957(.357SIG).
I FAILED TO EXTRACT EACH TIME CAUSING NEXT BULLET TO HANG UP AGAINST FIRED CASE STILL IN CHAMBER.
I DIDN'T SIZE CASES FROM STARLINE AFTER I RECEIVED THEM.  COULD THAT BE THE PROBLEM? BUT I MEASURED ALL DIMENSIONS BEFORE RELOADING AND EVERYTHING WAS WITHIN SPECS.  WHAT COULD BE WRONG?

It is always a good idea to full-length size any new brass. There can be tiny kinks in the mouth that can cause misfeeds. Also with Starline brass, its thicker nature may cause some problems in a tight chamber.

I have found some Starline brass has to be sized to be usable, .45 LC is one example. Otherwise I use almost exclusively Starline, and have very good luck with it.

Thanks Bill and Will,
  now the problem is occuring with several different factory loads(Gold Dot, Winchester, Hornady XTP and Corbon)!  The extractor seems fine and functions when I hand operate the slide.
But I keep getting a fired round that stays in the chamber while another rd. jams against it from the magazine.
 any ideas besides the extractor?

Bob

Sounds as if the chamber needs a little polishing. James Gates outlined a way of handling that on this site. You could run a search on polishing chambers and get it.