Do you have the rail mount sight or directly to reciever
Below is the starting steps to getting every thing tight and stay tight.
remove the sight and clean it , screws and holes should be free of any oil. Loctite does not like some alloys and will not cure correctly.
1. a torque screw driver and good quality bits
2. Loctite 222
3. Loctite primer, most plated , anodized, aluminum, parkerized parts do not cure well with out the primer.
See if ruger has a spec for the screw torque. 20inlbs should be enough.
If your screwing into aluminum and it keeps coming loose the threads might be fubar already.
Its not hard to pull the threads when tightening.