Cabelas carrys Browning magazines for the " A Bolt" for 42.99. Not sure if they carry the 300 Ultra mag magazines.Thay have the regular 300 mags. I don' t know if they are interchangeable or not.I just bought two BAR Mags from them and had them in a less then a week.Cheaperthandirt carries Browning mags but they run close to 50.00 there.Check Cabelas first.
www.cabelas.com
Looking under hunting/optics.
Ruger Redhawk