I was issued model 39, prior to your model. We always carried them +1, per S&W armorers instructions. As I have pointed out, most guns are designed for +1, like stated you can almost put another round in the magazine past the capacity. None of my Glocks had that play, and needed the but of the mag slammed to get a full mag to catch with the gun in battery. Plus add that when my wife's Glock broke that was one of the CS questions when I called Glock.