Vikram,

The advantages I have determined from personal use of borrowed sunken rib doubles are a forward light feel and no place for rust to accumulate unseen. It is so easy to run an oild rag in the space between barrels of a gun with no botto rib, or a single suken rib.

I have also used several ribless over unders and they too have the same advantages. So far I have not come across a totally ribless side by side. It would be nice to heft and shoot a few shots with an Alex Martin someday.