I built my semi-automatic M14 rifle many years ago. It has performed well although one small item annoyed me for a long time. While the rifle was built around a semi-automatic receiver from the now defunct Armscorp, all the remaining components were actual US Government M14 surplus rifle parts. Since the military M14 was a select-fire rifle, there was a cutout in the stock just above the trigger for the selector switch.
Besides being an eyesore, the large opening could allow dirt to enter the rifle right at the trigger group.
Some time ago, I had acquired a dummy selector from a shop that was closing it’s doors. The selector switch is mounted to the the stock and is for appearances only. It has no influence on the function of the rifle.
It has the original “A” marking that denoted that the rifle was set to fire on full automatic.
The switch can be pushed in and rotated…
To the unmarked semi-auto setting.
Myopicvisionary 
The selector cut out found on GI stocks can be filled with a non-functional kit as pictured, or you can fill it in with epoxy/wood etc… Sage international offers an aluminum cover for their EBR chassis, and the Blackfeather RS is delivered without a selector cut out.
I considered filling the cut but I thought this looked better.
Yep, it looks great.