If you go with Glacier Guides in Alaska, who had a notable string of #1 record book animals year to year, then the answer was, "as big as you can handle.... 375HH minimum."
Personally, my personal minimum would be a 375HH, in practice I would use a 416, as I am not interested in minimums or "just getting by."
Of course, the ultimate "fall back" answer is "whatever the legal minimum is" should bethe acceptable minimum, then again those folks (state game and fish) are in the business of selling licenses and the lower the minimum, the more potential applicants.
BTW, as a side note, I don't care if the rifleman is competent or not, start down that slippery slope and pretty soon you'll have someone claiming to possess the high end of excellence and justify hunting them with a 22LR or 223 or spear --- an easy conversation when one is 3,000 or more miles away and sitting at the fireside computer.
Good luck with your theoretical exercise.
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Never Go Undergunned, Always Check The Sight In, Perform At Showtime!
Good judgment comes from bad experience! Learn from the mistakes of others; you' ll never live long enough to make them all yourself!
I would put the minimum grizzly round at the .308 Winchester. A good 180 grain premium bullet will do the job on a broad side shot.
My personal choice would be the .375 H&H magnum. I wouldn't consider that the minimum though, as some people suggested. The .375 with something like a failsafe or triple shock bullet should bust up a grizzly pretty good lol.
I'll let you know, after I shoot one with the new CZ 550 safari I'm getting!
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Good Medicine for Anything with Fur...
Remington 700 CDL (30-06)
Harris Ultra Lite Bipod
Leupold VXIII 4.5-14x50mm Scope
Winchester 180g Failsafe
Myself, I wouldn't hesitate to pack my trusty field proven .338 win mag shooting a premium bonded bullet like the Federal High Energy Trophy Bonded Bear Claw in 225-250 grain. Will this calibre do as quick a job as the 375 H&H? maybe,maybe not but Im confident my rifle will break him down reasonably well and safely!
If I was paying $10k+ for a hunt, there is no way a "minimum legal" or "get by" cartridge is making that trip. Alternatively, in a "no cost" or backup arrangement, there is no way those cartridges are going either. I doubt you could find a guide who would take you on a brownie hunt with a .308, for good reason. I say .375 H&H, but since I have a .416 that would be the gun taking the shot.
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"A hunter should not select a caliber and bullet that will kill when everything goes right, rather,
should choose ones that will kill when everything goes wrong."
"Recoil lasts a second, but gravity lasts forever."
If I were selecting a rifle for a back-up type, charge stopping, situation then I would absolutely bump up my minimum. The .308 won't sufficiently break through heavy bone to STOPa charge. I think that the best back up gun in this situation would be the Marlin 1895G loaded with Garrett's unstoppable 45-70 rounds. He claims that they will shoot through a grizzly nostrils to entrails. You won't need anything more than that lol.
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Good Medicine for Anything with Fur...
Remington 700 CDL (30-06)
Harris Ultra Lite Bipod
Leupold VXIII 4.5-14x50mm Scope
Winchester 180g Failsafe
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If you can't beat them, join them... then once you lure them into a false sense of security, jump on their back and beat them to a bloody pulp.
minimun for grizzly/brown bear
