When you screw a handrail to the top of a balustrade you can at times avoid an ugly putty hole covering the screw by driving the screw in from the other side of the vertical post. But when you go into the wall, you may not have a choice.
Phil from Ingersoll, Ontario has an interesting suggestion if you find no other way to hide this screw.
Cut a cap off the top of the handrail, drive the screw in and then glue the cap back on. If you get a good fit on the cap, it all looks great.
Here is a working tip. When you cut the cap off, you will remove wood the width of your saw blade. When you bring that cap back down, it won't cover all of the handrail because of the removal of that waste on an angle. The trick is to make the handrail too long by the width of the saw blade. Then cut off the cap. Then cut off the length of the handrail removing what sticks out beyond the cap, which will be about the width of the saw cut. Now the cap should make a perfect fit to cover the hidden screw.