Magnetic recording cartridge including magnetic recording medium having a variation in width

A magnetic recording cartridge comprising:

• a magnetic recording medium having a base layer;
• and
• a reel, wherein
• a loss modulus at 65° C. of the base layer is 0.40 GPa to 0.01 GPa, the magnetic recording medium is wound around the reel, and
• when a variation in width is measured over an entire length of the magnetic recording medium after storage at 65° C. for 360 hours,
• a sign of variation in width Δout on an outer side of winding is a positive sign or a negative sign and a different sign from a sign of variation in width Δin on an inner side of winding, and
• the variation in width is 0 ppm (parts per million) at any position of two portions that are positioned opposite each other with respect to a center line of the entire length of the magnetic recording medium in a case where the entire length of the magnetic recording medium is divided into four portions by dividing into four equal parts.