I have tried Retumbo in my Weatherby and unless you are going to shoot 200grn bullets or better I would not recommend it. For your 180's try H1000, 4831, 7828, or N560. All of those have shown good results for me with 180 and lower weight bullets.
I agree with the others. Retumbo is a bit slow in the 300wby. It does fine in bigger cases like the 300ultra with 180s but theres better powders in the wby. My two go to powders are re22 and 7828