Whether top ribs are necessary or not depends on the shooter's preference,naturally.
I was referring more to the side ribs on OUs and the bottom ribs on SXSs which create a hidden rust trap, not to mention the weight they add. And there is that tin smithing bit which seems to go contrary to all the precision work on the rest of the gun. There is also the strange practice of externally file striking the barrels to lighten them AFTER the ribs are laid, which by definition must lead to non concentric barrel walls, perhaps this is what Robin Brown had in mind when commenting about strength in the quotation below.
Dewey VIcknair on his site has pics of the rust revealed when ribs are removed for relaying. There are interesting pics here
http://oplognosia.com/?p=12389of the Alex Martin ribless SXS and a horrifying pic of a SXS with a burst. The rust weakened barrel burst, blowing off the ribs and bursting the other, also rust weakened barrel. I photographed the user's left arm too but that was too shocking to show.
Here is an excerpt re the Martin ribless guns made by A.A. Brown. The writer quotes one of the Brown gunmakers comments about ribless guns:
"Robin Brown explained that the Browns had made "many of the ribless guns for Alex Martin" and many of the XXVs sold by E. J. Churchill. Alex Martin advertised that its ribless guns were "lighter, stronger and better balanced than guns of ordinary construction." Other advantages claimed were: 1) A quarter pound of useless metal is removed. 2) Removing this weight from the barrels makes the gun lighter forward, giving the left arm less work, more control, and an easier swing. 3) The usual hollow space between the barrels in which corrosion can take place undetected is eliminated. Guns in which the barrels were constructed with spacers at the breech, muzzle, and mid-barrel have a long tradition with Scotland's gunmakers—both Daniel Fraser and James MacNaughton made them."
What is said applies I think to the side ribs of OUs.
