RR,
Cor-Bon has some loaded 125 & 150 gr. hunting loads. I'm guessing that the bullet would need to be a real soft one for slow speed expansion. This is the only problem I see with this .300 Whisper. Im going to be calling JD at SSK and get their opinion and a load for short range deer huning. He invinted the round so he ought to know.
I did some reaserch last night heres some quotes I read:
For small whitetail deer, JD's recommended bullets to me (in order of preference) were: 125 gr NBT, 125 gr Speer TNT, and 130 gr Horndayd SSP. For supersonic hunting loads, he rec'd H110/W296/N 110, or AA 1680. In my 12" VVCG barrel, I easily get 2200-2250 w/ 125-130 gr bullets and H110 or W296. (My personal loads--all use Rem 7 1/2 primers and brass from SSK: 125 gr NBT/19.0 gr H110/2.462" OAL/2254 fps; 130 gr Hornady SSP/19.5 gr WW296 OR 19.5 gr H110/2.065" OAL/2200-2220 fps.) It's a very good hunting round that's amazingly efficient. 
The 300/221 looks to be a ballistic twin to the 30 Herrett, a legendary deer round. I killed 2 whitetail deer w/ mine last year.
The 125 Nosler BTip is the bullet of choice and will expand well at Whisper velocities. The 125 Remington bullet will not.