There were lots of different approaches to this. It is most often seen on heavy barreled rifles, allowing the architecture to be less bulky. Two Freeport, Illinois makers, Rudolph Pelck and John F. Dittmann, used a flat key with beveled edges that passed through a matching dovetail cut into the underside of the barrel. The key was flush with the barrel, allowing the ramrod to lay right against the barrel and allowing the forend to be quite slender. Another Illinois maker, Henry P. Brunker, in Ottawa, used a cast underlug with a hole for the ramrod to pass through, and a slot below it for the key. These are keyed quite low on the forend. He only did this on rifles with 1 1/4" barrels or larger. I have a heavy barreled target rifle by George T. Abbey, Chicago, that has the most unusual cast-steel barrel I have seen. It is octagon, but could best be described as "lobe shaped", with the bottom flat quite narrow and grooved for the ramrod. The key passes through a slot in the barrel on this one. All of these are high quality rifles. The absense of an underrib was for architectural reasons, not to save money or material.
