Still pondering the .300 Cana, with more paper bench racing.
With RL25, the .300 Win Mag case holds .896gr of powder for every grain of water of its max capacity.
.300 Win Mag = 86.4gr of water
.375 Ruger = 94.6gr of water
Thats a gain of 8.2 gr of water. So lets say it will be a gain of 7gr after the neck down takes place (the .300 RUM has 1 gr less than the .375 RUM). Ok I averaged all the loads for a 200gr bullet listed in my Lyman manual, and I come up with it gains 39.6 fps for every gr of powder.
So .300 win mag has a max load of 77.5gr of RL25, so with the new added capacity, I get 84.76gr of RL25. Thats roughly 7 more grains of powder. So 7 x 39.6 is 277fps. So add that to the 2901 of the RL 25, and I come up with 3178 fps with a 200gr bullet. So in a sense, I recreated the .300 Wby, minus the belt and in a 30-06 length action.
Disclaimer: I by no stretch of the imagination, expect this to be accurate, and no one should even think of trying the loads I have listed in this post. This was imaginary fun.