I would use a 125 Nosler BT and either H4895 or H4198 at a velocity of 2500 to 2600 fps. Recoil will be minimal and the 125 BT works really well in that velocity range.
Any 12 year old should've just fine with any 150 gr loads out of the .300 savage it's a soft kicker! MAYBE just use book starting loads for powder of choice.