USAFTurkey--- In the Gundecoy post you will see a photo of my NEF 20ga. I did the same thing -- Original 12ga. sent back for a 20ga. that came thru with a rib on it. To fit a 20ga tube on that 12 ga. receiver the outside of the 20ga tube diameter must be the same as a 12 ga. ( This is what I could see that the factory did to mine-- I'm no gunsmith) With the bore being 20 ga. Thus the thickness of the walls of the tube is thicker than the average 20 ga. To me it's plenty+++ thick for a gunsmith to drill and tap for a scope mount. I really doubt that the rib in any way is scope mountable- I do not think the rib on mine is metal. I have a peep site on the rib now but maybe a Red Dot in the future. P. S. If when done, you stick a Tom's beard like I did with mine , it will turn that 20 into a Gundecoy and will draw in Toms without even calling---- good luck--- Web
