RE: 300 Ultra Mag for Brown Bear
It's obvious he's worried about bullet failure!!
Use 200 or 220 NP's and get good with that load/rifle and you will be just fine... TSX's may also be good, but i don't have any experience with them on big bears, like i do with NP's...
If i had your rifle and liked it and "was use to it", i'd not buy something new and start over now....
DM