I'd absolutely agree about the state of the spring. If there's no pressure on the trigger, the hammer should fall into the half cock notch as it drops. That suggests the spring isn't bearing heavily enough on the trigger. Likewise, if the tip of the trigger has become worn (often by clipping half cock notch) instead of hard surface, you end up with a rounded edge will is easy to slip. I had somethng similar happen to my original Remington in Valencia at the European Zone Championships where the trigger went so light it wasn't controllable. On returning and rehardening the trigger and tweaking the trigger spring, I shot a 95 with it (10 points better than Spain) two weeks later...