Album: Damascus Barrels & Ribs
From "The Gun and Its Development: With Notes on Shooting" by William Wellington Greener, 1885 - Ribs are forged from rods twisted in the same manner as described for the manufacture of Damascus iron. They are then forged to the required shape upon a grooved anvil. Plain iron ribs are used for very common guns, in which case they are rolled for the gun to the required shape.
For more information see http://docs.google.com/Doc?id=dfg2hmx7_293fxzspwc3 Special thanks to Charles A. Herzog Sr., Craig Smith, and Paul Stevens