I claim the ornamental design for a magnetic gun holder, as shown and described.
FIG. 1 is a perspective view of the exterior of the magnetic gun holder.
FIG. 2 is a top plan view of the exterior of the magnetic gun holder.
FIG. 3 is a front elevational view of the exterior of the magnetic gun holder.
FIG. 4 is a side elevational view of the exterior of the magnetic gun holder.
FIG. 5 is a bottom plan view of the exterior of the magnetic gun holder.
FIG. 6 is a perspective view of the interior part of the magnetic gun holder with the exterior removed for ease of illustration.
FIG. 7 is a top plan view of the interior part of the magnetic gun holder.
FIG. 8 is a front elevational view of the interior part of the magnetic gun holder.
FIG. 9 is a side elevational view of the interior part of the magnetic gun holder; and,
FIG. 10 is a bottom plan view of the interior part of the magnetic gun holder.
The broken line showing in the figures is included for the purpose of illustrating portions of the magnetic gun holder and forms no part of the claimed design.