The ornamental design for disk saw felling head horn, as shown and described.
FIG. 1 is a perspective view of my design for a disk saw felling head horn, with broken lines illustrating environmental structure and forming no part of the claimed design;
FIG. 2 is a rear elevational view of the disk saw felling head horn;
FIG. 3 is a front elevational view of the disk saw felling head horn;
FIG. 4 is a bottom plan view of the disk saw felling head horn, with surfaces that would not be seen in use shown in broken lines, for the purpose of illustrating, and forming no part of the claimed design;
FIG. 5 is a top plan view of the disk saw felling head horn;
FIG. 6 is a left-side elevational view of the disk saw felling head horn; and,
FIG. 7 is right-side elevational view of the disk saw felling head horn.