Just purchased a early 11/89 G-19 in nice condition. Last night I cleaned the pistol, and took a couple of boxes of different loads to the range. the gun ran through a box of 115 FMJ and was smooth and on target.  I switched to S&B 9mm and after a couple of runs I had what I thought a misfire,I racked the slide and the next pull seemed that it required an extra 5lbs of pull. This continued the rest of the session. I've shot thousands of rounds of S&B through my G-17 including rounds in this lot. nary a problem with a stiff trigger. Any idea's as to what it might be ? Thanks