Frankly, I'm with Franc on this one. A perfectly fitted lug on the underside of the action seems to be incredibly difficult to make. Also, it's easier to clean the action if there is a cutout for the lug. I suspect with or without was merely a mark of distintion of makers. Had there been a real benefit of a hidden lug the Birmingham makers would have adopted it. My guess is the gun with the cutout is slightly stronger due to leaving more metal on the lug.

John McCain is my war hero.