This is mostly of concern to those of you who want to re-barrel a gun, or have one built. Or just want to become a better person. Anyway:
Just about all barrel makers turn out six contours, or profiles, ranging from #1, which is light sporter, to #6, which is heavy bull. Number 2 and 3 are magnum, number 4 is varmint (a heavy tube, but with some taper), and numbers 5 and 6 are bull barrels with little or no taper. What is more important than the arbitrary numbers of the barrels is their weight.
Forty years ago when I started having rifles built, I decided that more weight in the barrel was better than less, and I’ve seen nothing in the past four decades to change my mind. A bit more weight up front makes a rifle easier to hold steady, easier to swing and keep swinging, less prone to walking as it heats up and, in the case of a big rifle, a big barrel can remove a lot of the kick and cut way down on muzzle jump. Two prime examples of this last are the Remington Model 700 in .375 H&H and the Ruger Model 77 Mark II in .416 and .458 Lott, which are fitted with major honking barrels at the factory and profit mightily thereby.
When E.R. Shaw built my .30/06 they suggested a Number 1 contour which is standard for that cartridge, but I noted that they make a Number 1 ½, which they call the Magnum contour, and insisted on that. I’ve never regretted the choice. The rifle not only shoots like hell but is very easy to shoot, and I think that extra weight is what makes the difference.