"Drop-in" means the frame does not have to be altered. The result is a gap between the safety and the frame because of the curved edges of the frame. The only modifications that might occur is the fit between the nose of the grip safety and the trigger bar, which testing after installing will determine. The grip safety must prevent the trigger pull from firing the gun when it is not being gripped, and must allow the trigger to travel far enough to fire with the safety gripped.
