have searched DoubleGun BBS without success for MF catalog reference about their swamped rib. did locate such a reference on NitroExpress; about one third way down the page is a post by DORLEAC (post #248382). it shows two pages of old catalog with fig.#1 showing the central fixture of the one piece rib...along with corresponding text. (unfortunately for me, it might as well be in greek...) http://forums.nitroexpress.com/showflat.php?Cat=0&Number=248297&Main=248074

in this discussion that revolves around nomenclature and more precise definitions of terms, i think it would be useful to differentiate between top & bottom two piece ribs (which might be "swamped" by narrowing their width in mid-section), and these one piece central mounted ribs as used by many french makers.

i have never actually seen any of the ribless english guns (alex martin/a.a.brown). but photos show what i suspect is a central rib of 2-3" at the muzzle, and 6-8" at the breech. can anyone say if those are two piece type, or something more like the french rib?

"it's a poor sort of memory that only works backwards."
lewis carroll, Alice in Wonderland