I USED A 646, WITH THE FULL UNDERLUG , IN IDPA UNTIL THE RULE CHANGE ON THE POWER FACTOR. MINE WAS 100 PERCENT RELIABLE--NEVER POLISHED THE CHAMBERS. I DID CHANGE THE SPRINGS, INSTALLED EXTENDED FIRING PIN AND BACKED OUT THE STRAIN SCREW 1 FULL TURN AND LOCKTITE IT IN PLACE(GREATEST TRIGGER EVER ON A REVOLVER I HAVE OWNED). I ALSO EXCLUSIVELY USED THE .040 MOON CLIPS, WINCHESTER BRASS, 155 RN LEAD LOADED TO 132 PF. I REALLY ENJOYED A LOT OF SUCCESS WITH THIS SETUP. AFTER THE RULE CHANGE SHOT ONE CLASSIFIER WITH 170 PF AMMO, STAYED EXPERT WITH IT BUT IT WAS NOT VERY ENJOYABLE TO SHOOT.