i just purchased a savage 111 300 win mag. with a simmons blazer 4 to 16 scope. i have no knowledge of this scope and it has a knob on the left side that when you turn the knob it has a post that flips up. what is that for? i can't find any informatiom on the net reguarding this knob. will this scope hold up with this 300 win mag cal? thanks bruce