The reason for and under rib?

[Kurt]

I am not a builder. I saw a plains-type rifle without an under rib, the thimbles attached to the bottom of the barrel. This made me wonder why under-ribs were used, assuming materials were scarce. Was this simply because it made a better-looking rifle?

[rich pierce]

With an underrib, a half stock gun keeps the web or space between the barrel and ramrod hole.

[Kurt]

Okay, you got me to think, and I realize the pins or wedges and underlugs need to have space or they would have to go through the bottom of the barrel. Thank you.

[Scota4570]

To put it another way... Say you stuck the thimbles to the barrel directly.   Without out the lift provided by the rib, the rod has to bend bend to enter the ramrod hole. 

I use the thimbles to guide the ramrod drill.   

You could set the barrel thimbles up on spacer blocks.  That looks as bad as leaving the rib off though.  I have seen some low budget guns that do it that way. 

[Hungry Horse]

 I own two late 1800’s percussion rifles that have no under rib. They are both relatively small caliber and use a 5/16” ramrod. One has a barrel that is 36 caliber and is at least an inch across the flats. The barrel wedge on that one goes through a slot in the barrel. The other is a 40 caliber double, and although it has a traditional rib on top of the barrels, the bottom is sealed with a strip of thin sheet metal soldered in place. The double has thin barrel key, and the 5/16” ramrod bends around it. So never say never.

Hungry Horse

[Daryl]

The old 12 bore double I once had, had the rod, as typical with SxS guns, fitting to the under rib joining the barrels. The rod groove in the forend was just a rounded groove in the middle
of the forend. The barrel wedge escutcheon, attached to the under rib had a hole in it the rod passed through and with the wedge slot in a projection below the rod's hole, placing it very
low on the rounded forend. This was an English gun built for the Americas, I assume.

[rich pierce]

The old 12 bore double I once had, had the rod, as typical with SxS guns, fitting to the under rib joining the barrels. The rod groove in the forend was just a rounded groove in the middle
of the forend. The barrel wedge escutcheon, attached to the under rib had a hole in it the rod passed through and with the wedge slot in a projection below the rod's hole, placing it very
low on the rounded forend. This was an English gun built for the Americas, I assume.

The Sharon Trade Rifle used the same setup. Thimbles soldered to barrel and the ramrod goes through a thick blocky underlug in the forestock area which has a hole through it. At the very bottom of the underlug is a slot for a wedge.

[Elnathan]

Mostly stylistic concerns, I think. European halfstocks from the 18th and 19th centuries usually just have the ramrod pipe soldered directly to the barrel, though the way the base of the pipe is formed the ramrod is held a little bit away from the barrel instead of being smooshed right up to it.  I own an original with this arrangement, currently in storage, and the ramrod goes in more or less straight, IIRC - certainly no radical bend. Post-Civil-War-era muzzleloaders sometimes did away with the underrib too, mostly for economic concerns, I think. At that period muzzleloaders were all just cheap barn guns, and there were probably few people interested in spending money for features  beyond what was absolutely necessary.

The Spanish and German fowling pieces with no underrib used barrels with big breeches and lots of taper. With a less tapered barrel, such as was more typical of the 19th century, the geometry might not work so well, so that might explain the introduction of the underrib. The use of underribs on double shotguns might also have been a factor.