It probably could be done but keeping the mag in the rifle 100% of the time might be hard unless you have a monster magazine release latch. There is a reason they pinned the floorplate on the big magnums. ~MuirI don't know of anyone doing bottom metal which ch would allow that in a magnum length action I am afraid.
It could be done as a custom thing but the price may be a little high. You would obviously also need a mag from another rifle to use or have a custom one made up.
They're all 30-06 length except the 338 lapua which is significantly wider, isn't belted, and is if a different shape. I honestly don't know if it'd work
Only a call or email to PTG will anyone know for sure. Cz did offer the Win mag in both actions but only the lapua in the mag/safari. Accurate Mag does make 375 H&H mags in the same length. The ribs on the side of the magazine won't let the 375 fit in a standard win mag. Ai pattern mags in single stack are the same width between 300 and 338 they make three different lengths.
Bewsher500 the feed lips are different lengths between 300 and 338 had feeding issues using 338mags for the Win. Accurate Mag does make the long pattern for win mag 3.850.
http://accurate-mag.com/magazines/
They get about 1000 emails a day. Send another until you get a response.~Muir