Good eye!
It's a 300WBY Mark V. I've had it for almost 30 years. Originally the action was fitted in a black synthetic stock. The synthetic stocks back then were good but not even close to how good the Graphite composite stocks available nowadays. A couple years ago, Bell and Carlson came out with an aftermarket graphite composite stock they called the "Medalist". It contained a solid aluminum bedding block, was lighter and stronger than the original. I bought one and it fit PERFECT. It did increase the accuracy of the rifle and reduce the recoil significantly. One of the best aftermarket improvements I've ever purchased.
I used 180gr Accubonds and they worked perfectly.