I can't see why the 6mm BR or 6.5mm Norma BR wouldn't be useful for deer - provided you loaded them with an appropriate hunting bullet at an appropriate velocity. .243 is a 6mm, 6.5 Swede and .260 are 6.5mm, and are all considered good deer rounds.
Whether your rifle is a good one for hunting with is another issue.
As far as your FP10 issue, Zerodefect, if you want that rifle with a different caliber barrel on it, you could do one of two things: call Savage and see if they'll put one together in your preferred chambering, or buy another barrel in your preferred chambering, swap it out for the .308 barrel, and sell your unwanted .308 to recoup part of the cost of the new barrel. Can be done at home on a Savage. Instructions and demos are on Youtube, believe it or not.
