Bull barrels are ~.800" at the muzzle, big bores(44mag, 444, 45-70) are also about .800" except the 45 Colt which is ~.700" and the 500S&W which is ~.870", but are not considered bull barrels. All of H&R's modern standard barrels have a heavy contour, up to .750", so heavy many incorrectly call them bull barrels, just the way they make em.
If you look at the accessory barrel list, you'll see which barrels are called bull barrels, some of the descriptions on their site will also describe them as heavy, like the 45-70 Ultra Hunter.
Tim
http://www.hr1871.com/Support/accessoryProgram.asp