My neighbor picked up a cheapy Henry lever .22 the other day and asked me if I'd sight it in for him. Danged if it doesn't shoot 8 inches right at 25 yds. So I look the sights over and see that windage and elevation are both adjusted at the rear sight. Well, I take a brass punch and try to drift the rear sight in its dovetail over to the left... and try, and try, etc. It WON'T move!!! What am I doing wrong here? Is there something that I don't know that I should?