Running 147gr plated lead at 880fps. Ejection is very weak. It's like shooting a .22 and I'm getting insanely tight groups too. I'm shooting trijicon HDs at the moment and point of impact is just about perfect. Front sight is wider than optimal but working for me. My only concern is the ejection. Brass practically dribbles out.I use the stock spring at 130 - 135 power factor for IDPA with no issues. Personally 130 PF using 125 gr bullets run like a hot knife through butter. Why bother changing the springs. The gun sights are set up for 124/125 gr bullets. I would ignore the 115 gr bullets for competition.
At around 1,115 fps the gun will run just fine with factory springs.