Without pictures or more information about exactly where your hole is, I'd guess it's for mounting a Marble's (or other maker's) tang sight.

 

From what I was told by a Remington collector the two large holes on the right were used to mount the receivers to fixtures for machining and nothing else. The Model 16 had them as well, but since it was a two-piece receiver there was one on the left side. I have a Model 16 missing the plug screw for the hole on the left side by the chamber, I found it is the same diameter but a finer thread than those used on the Model 24. When I got my first Model 16 that hole without a plug confused me, I had no idea what type of screw went in it, there appears to be no special machined feature in the hole that would require it for access, or anything that needed a screw, so it must just have been for fixturing.

 

Thanks for that info.

 

The rear plug has a center pin sticking out. It lines up with a hole in the outer magazine tube and holds it in place in the rear of the action. You have to remove it before
removing, unscrewing the outer magazine tube from action.
Part 54.