The ornamental design for a firearmbuttstock, as shown.
FIG. 1 is a front isometric view of the firearm buttstock;
FIG. 2 is a rear isometric view of the firearm buttstock of FIG. 1;
FIG. 3 is a front view of the firearm buttstock of FIG. 1;
FIG. 4 is a rear view of the firearm buttstock of FIG. 1;
FIG. 5 is a left side view of the firearm buttstock of FIG. 1;
FIG. 6 is a right side view of the firearm buttstock of FIG. 1;
FIG. 7 is a top view of the firearm buttstock of FIG. 1;
FIG. 8 is a bottom view of the firearm buttstock of FIG. 1; and,
FIG. 9 is a right side view of the firearm buttstock of FIG. 1 attached to a firearm in the form of a rifle.
Portions of the firearm buttstock shown in broken lines in FIGS. 1-8, as well as the firearm shown in broken lines in FIG. 9, form no part of the claimed design.