I second thisAccurate makes a "10 round" .300WSM mag (holds 7 WSM cases). You can add an alloy mag extension that might get you to 10.
The .300 WSM magazine expands the short action double stack line to accommodate WSM calibers, SAUM calibers and the new 6.5 PRC. ITEM CAP W L H .CAL .CAL MAX OAL 00100- 0006 DSSF 3RD .97 3.055accurate-mag.com
MDT's new Short Action Mag Extender lets you add +2 capacity to your AICS metal short action magazines and gain an advantage in high round count competitions. NOTE: MDT 10 Round Mags Require Spring Kit Found Here NOTE: Not Compatible With Poly Mags NOTE: Not for MDT 6BR/Dasher Mags or Mags w/...www.shortactionprecision.com