The reason that you won't get much feedback on loading down a 300 win mag to 308 or even 30-06 is that most of us have additional rifles in smaller calibers and use those rather than load down. Loading down can be tricky in high volume cases with secondary explosion effects a remote possibility and loading under minimum can cause as many problems as loading above.
RockyMtn offered a very good solution with using non-frangible bullets like Barnes TSX's, Swift Scirroccos, Hornady Interbonds, Nosler Partitions, etc etc
This was a shot through the front shoulders on an Elk with a 300 win mag and 180 gr TSX at 250 yds going in and coming out
You can eat right up to the hole and no gore
It would have been even less through the ribs but he needed to be anchored right there
Load a 200 gr TSX at 2850 fps (full load but a couple of grains below max) and you will get full use of your caliber with not much meat loss. Probably excellent accuracy also