As difficult as it will be to find dies and brass for the .300 Whisper, you might consider down loading a .308 Winchester - like Briman suggested. I have used powders like N-110 and IMR 4227 to fire form cases in the various Ackley Improved calibers. In the 30-06, for instance, the fire form load is going about 2,000 fps and has very mild recoil.Also agree with the bullet choice - 125 Ballistic Tips, as explosive as they can be at higher velocities, could be just the ticket at reduced velocities. Around 2100 fps MV would be about right, I would think. Could also do the same thing with a .270 - and load the 110 V-Max to reduced velocities.

You could then increase the velocity of the load as she grows and, maybe someday, be up to full throttle.

Must be great to have a little hunting buddy, up at the crack of dawn, ready to go. My son likes to hunt; but, like yours,it isnearly impossible to get him up at zero dark thirty.