The ornamental design for a seat back guncarrier, as shown and described.
FIG. 1 is a perspective view of the seat back gun carrier comprising a first and second carrier sling.
FIG. 2 is a front elevational view of one carrier sling of the seat back gun carrier, the front elevation view of the second carrier sling being substantially identical thereto.
FIG. 3 is a right side elevational view of one carrier sling of the seat back gun carrier, the right side elevation view of the second carrier sling being substantially identical thereto.
FIG. 4 is a left side elevational view of one carrier sling of the seat back gun carrier, the left side elevation view of the second carrier sling being substantially identical thereto.
FIG. 5 is a top plan view of one carrier sling of the seat back gun carrier, the top plan view of the second carrier sling being substantially identical thereto; and,
FIG. 6 is a bottom plan view of one carrier sling of the seat back gun carrier, the bottom plan view of the second carrier sling being substantially identical thereto.
The broken lines of FIG. 1 showing the environment of a car interior and firearms form no part of the claimed design. The remainder of the broken lines show portions of the seat back gun carrier that form no part of the claimed design.