Remington M11 with ribbed barrel

[harold]

I ran across a Remington M11 US marked
Shotgun today in really nice condition.
The shotgun had a solid rib on the sight plane.
It appeared to be factory original finish and wood.
Is this a bubba project or was this a variant style
Of the M11 . Just curious if the experts could help me identify
This for me. I have found nothing on the web like it.
I am considering adding it to my collection , if original .

[scosgt]

Was the barrel serial numbered to the receiver?
Did it have the US or bomb on it?