Joe is correct. Even by the mid-1800s rolling mills were in operation. PeteM has an image of a patent drawing on his site, but I don't know the date.
Engines Of War: or, Historical and Experimental Observations on Ancient And Modern Warlike Machines And Implements, Including the Manufacture of Guns, Gunpowder, and Swords with remarks on Bronze, Iron, Steel, &c. Henry Wilkinson, M.R.A.S. London
1841p. 70 Part III On The Manufacture of Fire-Arms, And Modern Improvements.
http://books.google.com/books?id=0XJeF_oa3SMC For the finest...barrels, a certain proportion of scrap steel, such as broken coach-springs, is cut into pieces and mixed with the iron by the operation called puddling, by which the steel loses a considerable portion of its carbon, and becomes converted to mild steel, uniting readily with the iron, and greatly increasing the variegation and beauty of the twist. In whatever manner the iron may be prepared, the operation of drawing it out into ribands for twisting is the same.
This is effected by passing the bars, while red hot, between rollers until extended several yards in length, about half an inch wide, and varying in thickness according to whichever part of the barrel it may be intended to form: these ribands are cut into convenient lengths, each being sufficient to form one-third of a barrel...
