Up in Canada. .303 was THE cartridge for a long time, like our 30-06. Moose, elk ,caribou, black bear & even griz. Still pretty popular, more than down here. Too bad it's been losing ground to all the new super-magnum craze. I've seen some real beautiful custom sporterized SMLE's going for pennies the last 10 years or so. Ammo mfrs offer very little in hunting ammo today; damn shame.
I spent some time years ago in B.C. in the bush and the .303 was still in use, although fading out as people were buying new sporters in the usual hunting calibers. Just like all of us, most wanted a new rifle, so the sporterized .303 was relegated to the rack.
As mentioned, the natives on the Reserves were still using them successfully. Deer, bear, and moose were successfully killed.
One mistake I made at the time was not buying a Long Branch Arsenal SMLE and bringing it back to the States.
While I don't agree with Danjal that it is the equal
of the .30-06, because it sits between the 170/.30-30 and 180/.30-06 energy-wise - with a velocity 240 fps slower (180-gr) than the '06. Still it is basically equal to the old .300 Savage or 30-40 Krag, both of which had a really good big-game rep back in the day. Therefore it is more than adequate enough if the distance is kept reasonable. Big long heavy .30 cal bullets work fine at medium velocities - even basic cup-and-core bullets.
Sighted in 3" high at 100 yards with the factory irons should put you on zero at 200 yards and 4.5" low at 250. I don't know if I would push it much beyond those ranges, all things considered, but a SMLE should do the job good enough should you want to try something different than the .300 Mag. They really are interesting and neat rifles.