That it cannot be safe in a TC Contender is in my opinion a misconception. There have been quite a few barrels made by custom makers in both .250 and .300 Savage. I owned a .300 Savage myself made by SSK Industries. I discussed it with JD prior to having it made and he indicated he felt factory ammo to be safe but cautioned me to stay a bit below max loading data in some manuals. It did work but I didn't feel it performed well enough in the 10" barrel I had rechambered to be of value. You can get as much velocity safely from a .300 Whisper as you can the Savage in a ten inch barrel. I'm sure that had I gotten a 14" barrel rechambered instead of a 10" I'd have held onto it.
Still I think both are sub optimum in the Contender and a better fit for the Encore. If you want that level of performance it would be wiser to chose the .257 JDJ and .309 JDJ rather than the two Savage rounds.
I do not believe that SSK Industries has ever chambered or rechambered a barrel to a cartridge for which factory ammo was available if that factory ammo was not safe in it for a Contender or for that matter any other firearm. JD is an extremely safety conscious person.