Looking at all my old loading manuals from the 40's and 50's/60's, all of them cite the 180 grain as the bullet of choice for the 300 Weatherby Magnum, which was brought out just after WWII.....

The loading manuals go on to say that the 180 grain bullets shoot flatter than the lighter bullets and they all show the ballistic coefficient is higher as well.....

I load & shoot the same 200 grain flat base in my .338 Win Mag for the last 35 years or so and it's dropped an awful lot of deer and elk and bear etc....dead in their tracks and shoots extemely flat with authority.......

Hope this helps for whatever it's worth.......

Best...

Doug