The ornamental design for gun, as shown and described.
1. Gun
1.1: Perspective
1.2: Left
1.3: Right
1.4: Top
1.5: Rear
The model regards a gun; fig. 1.1 is a perspective view of the model; fig. 1.2 is a left side view thereof; fig. 1.3 is a right side view thereof; fig. 1.4 is a top view thereof; fig. 1.5 is a rear view thereof; the parts of the gun shown in broken lines are for illustrative purposes only and form no part of the claimed design.