The ornamental design for a competitionthumbgrip for a gun, as shown and described.
FIG. 1 is a perspective view of my new design for a competition thumb grip for a gun having a monolithic wing with precision alignment and shape for the thumb pad;
FIG. 2 is a left side elevation view of the article shown in FIG. 1;
FIG. 3 is a right side elevation view of the article shown in FIG. 1;
FIG. 4 is a front end view of the article shown in FIG. 1;
FIG. 5 is a rear end view of the article shown in FIG. 1;
FIG. 6 is a top view of the article shown in FIG. 1;
FIG. 7 is a bottom view of the article shown in FIG. 1; and,
FIG. 8 is a side perspective view of the article shown in FIG. 1 mounted in its intended environment of use (in phantom lines) on the left side of a gun in proximity to the trigger for a right-handed user.