I know this is a very old thread, but a March 1, 1906, Winchester ammo catalog showed up on ebay today. It shows they offered 8-gauge LEADER shells with loads up to 6 drams of bulk smokeless powder or the equivalent in dense smokeless powder and 2 ounces of shot.
March 1, 1906 03.jpg
If I was allowed to edit those old posts, I could replace the pictures lost to the Photobucket hostage taking.