Hell why not take it down to 9,3mm then you have a 450-366.

But actually the brass would be cheap and you wont need the extra voulume of the 45-120
as you could increase the pressure a bit in a new action. And now one would be able to try and shoot a 416 thru a 410. But perhaps it wound be able to perform in the higher velocities, but no one has specified the speed yeat.