1100 Stock to Receiver Fit

[Virginian]

The only way to close that gap will probably be to remove some wood at the bottom of where it mates with the stock. It apparently was made that way, and wrong if I do say so, because Remington stocks should interchange and fit with no issues. The solution is to remove some wood where the stock meets the receiver. Check to make sure you are getting a good fit on the bearing plate inside the receiver. Fold a sheet of paper and cut to fit and see if it opens a gap equally all the way around. If you do remove some wood, and the finish, be sure and seal the open wood pores when you are done. You can probably do it with a sanding block, just use relatively fine, say 200 grit or smaller, paper and smooth even strokes until you get the fit you want. A couple of final passes with 400 grit at the end. You want to change the angle of the whole mating surface, taking zero off at the top and your gap thickness at the bottom.
Good luck.