I'll check my Nosler guide when I get home; but Retumbo should be just great for the .300wby. Any of the slow burners (RL22,50BMG,8461) have a load; but I'll check when I get home.
"...I'd rather be tried by twelve than carried by six..."
My latest manual does not list Retumbo for any of the 180 gr. loads in the 300 Weatherby. It does lists a load for the Nosler AB 200 gr. bullet. Starts at 79 gr. and max is listed at 84.5 gr. for 2942 fps and 53,100 cup.
The manual is Hodgon's 2008 annual manual. They should have it on their web site.