I would like to add an additional ground bar to the panel. The panel is a Murray LC3040B1150. On the panel door it says to use the LX series ground bar and mount it on the right side under the neutral bus. I went and got the LX ground bar from the supply house. Problem is, none of the existing holes line up with the mounting holes on the ground bar. So I drilled and tapped one hole, and used an existing hole for the other screw mount. On the hole I drilled and tapped, I cannot get the screw to the proper tourqe of 24-30 in-lbs. Is there anything wrong with putting a locknut on the back of the box? Or should i just try a larger self tapping screw? Note, the black screws are not what came with the ground bar, they are the same screw size though, just longer. Had them in my parts box. Thoughts?