I've just read a couple of books about two English hunters who went on two "shoots," one in Somaliland and one in Alaska in the 1905-1907 time period.

For the African hunt the author listed their battery as:
Three 12-bore rifles,
Two double barrelled [sic] hammerless ejecting .500 expresses,
One .35 Winchester,
Two small .22 Winchesters,
One single barrel .350,
One .410 collector's gun,
And "a good shikar pistol apiece, 12-bore."

For the Alaska hunt they took "... '375 and a '256 Mannlicher ... our old 12-bores, a '35 Winchester, a '22 Winchester, and a '410-bore collector's gun."

I'm curious about the 12-bore rifles and, in search of information, I ended up at this site -- and it's been great fun lurking the past week or so. Anyway, were the 12-bore rifles like the shotguns of the day, but with rifled barrels? Were the cartridges similar to our slugs? The English hunters I was reading about used their 12-bores for lions, rhinoceros and brown bear. Thanks in advance for any comments or insights.