I claim the ornamental design for the gun sling, as shown and described.
FIG. 1 is a perspective view of a gun sling;
FIG. 2 is a front facing view of the gun sling;
FIG. 3 is a back facing view of the gun sling;
FIG. 4 is a side facing, perspective view of the gun sling;
FIG. 5 is a view of an end buckle of the gun sling;
FIG. 6 is a view of a second end buckle of the gun sling;
FIG. 7 is an enlarged partial view of the of the front of the gun sling; It being understood that the pattern shown in FIG. 7 extends the entire length of the gun sling; and,
FIG. 8 is a perspective view of the gun sling.
The portions shown in broken lines form no portion of the claimed invention.