I think your 7RM is fine. It will definetly kill a big brown bear. Heck a .22 would if you put it right in the eye or ear.
If I were going to find an excuse to buy another firearm for a browny hunt it would be a pre-2008 Marlin Guide Gun in 45-70. Hit that sob with a 500 gr bullet going 1400 fps and you'll see it go down.
Tom