Interesting "shotgun"! If you don't get a good answer here, ask on the Remington forum on www.rimfirecentral.com. Or the "Single Barrel and Custom Rifle" forum on www.doublegunshop.com/BBS.

I've seen quite a number of "Routledge bore" Remington .22s. None had factory ribs.

Was Mike Armstrong. Got logged off; couldn't log back on. RE-registered my old call sign, Mesa.
FNG. Again.
Mike Armstrong