If you buy a .300 win mag, why would you want to "download" it or bugger about with "managed recoil" loads? it sort of defeats the point of having one, doesnt it?
I know someone who uses one, when he hits a roe it many times it bursts the gut even on a good heart shot.
You seem to have asked and answered your own question here?
Q: "Why would you want to download it?"
A: "Many times it bursts the gut even on a good heart shot."
Plus it is a lot easier to download a 300 H & H or Win Mag to duplicate a 308 than it is to load up a 308 to duplicate a 300 H & H or Win Mag!
Makes perfect sense to me. A loaded down rifle with "Managed Recoil" loads off the shelf for everyday use on deer but with the ability, again off the shelf, with standard cartridges easily available in "foreign parts" to use on wild boar, elk, or for long range, 300 yard, mountain use on mouflon or the like.
And all this in a non-military calibre that isn't the virtually unobtainable in UK or USA calibres of 7x64 or 8x68.
A real "double duty" gun that can do two things well with the flexibility of these recent "Managed Recoil" loads that extend the cartridges' flexibility to truly be a useful deer cartridge in the UK.
The same reason I actually now download my 270 to about 2,700 to 2,800 fps with a 140 or 155 grain bullet now I'm mostly woodland stalking.