The ornamental design for the rifle magazine, as shown and described herein.
FIG. 1 is a side perspective view of a rifle magazine showing my new design;
FIG. 2 is a right side view of a rifle magazine showing my new design taken from the left;
FIG. 3 is a left side view of a rifle magazine showing my new design taken from the right;
FIG. 4 is a back side back elevation view of a rifle magazine showing my new design;
FIG. 5 is a front side elevation view of a rifle magazine showing my new design;
FIG. 6 is a bottom view of a rifle magazine showing my new design; and,
FIG. 7 is a top view of a rifle magazine showing my new design.
The broken line showing portions of the rifle magazine is included for the purpose of illustrating environment and forms no part of the claimed design.