A 7mm Remington chamber is larger than a 7mm Weatherby. The Weatherby case is about .050" longer but it is all in the neck. The Remington case is longer to the shoulder and to the shoulder neck junction. I've been using Weatherby cases in my 7mm for many years. I trimmed the necks and fire formed the Weatherby cases in my 7mm Remington.
Why what? Why I used Weatherby cases? Because that is what I had. But maybe I got a benefit I didn't even know I was getting. Almost every comparison I see of the 7mm RM and the 7mm WM the WM supposedly has a lot more case capacity. That certainly isn't from external case dimensions.