We claim the ornamental design for a magazine cap with sling loop, as shown and described.
FIG. 1 is a perspective view of a magazine cap with sling loop showing our new design;
FIG. 2 is a second perspective view thereof;
FIG. 3 is a front elevation view thereof;
FIG. 4 is a back elevation thereof;
FIG. 5 is a right-side elevation view thereof;
FIG. 6 is a left-side elevation view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof; and,
FIG. 9 perspective view of the magazine cap with sling loop attached to firearm.
The broken lines showing portions of the firearm are included for the purpose of illustrating environmental structure and form no part of the claimed design.