The ornamental design for a gunstock, as shown and described.
FIG. 1 is a perspective view of a gun stock showing my new design, the portion shown in phantom lines forming no part of the claimed invention;
FIG. 2 is a side view thereof;
FIG. 3 is an opposite side view thereof;
FIG. 4 is a top view thereof, the portion shown in phantom lines forming no part of the claimed invention;
FIG. 5 is a bottom view thereof;
FIG. 6 is an end view thereof; and,
FIG. 7 is an opposite end view thereof.
The broken line showing of aspects of the gun stock in FIGS. 1 and 4 is included for the purpose of illustrating environment and forms no part of the claimed design.