TESTING OUT THE CHEAPEST SQUIRREL HUNTING SET UP I CAN FIND!!! 

If u take that scope ring off there's a screw that takes that nub right out....that nub is for air rifles

Sonny you have a lot to learn.

$170 702 plinkster with a $50 Walmart scope and some $25 scope rings your good to go. Ill tell you i out about 500 rounds through the same hole with this exact setup