A swipe of shellac to the threads of the screw and then assemble the part was often used to keep screws from loosening.
It holds very well but can be disassembled w/o much difficulty if needed.
Some parts used to be assembled with Iodine placed on the threads of the screw(s). That will make the screw and the base part actually rust in there and they do not come apart easily! This was generally used on 'scope & sight mounts destined to never be removed.
But never say never.
There are some screws in some assemblies on some guns that just want to loosen with use.
The SAA grip frame screws are an excellent example.
They have used thin Nylon 'washers' under the screw heads and other sorts of locking methods.
The earliest of the pre-WW2 Marlin hammerless pump shotguns will loosen their full sideplate attachment screws often,,very often.
So much so that MArlin changed the design to include small locking type screws with them to keep everything in place.
Using a hammer to compact the threaded shaft of the screw itself ever so slightly can tighten the fit.
It's a very touchy technique to learn how to do and not ruin the screw itself. But it does work nicely and is very quick to do. Helps to 'qualify' screw slots that are just off a bit as well.
Best bet for the screws that like to walk out is a thread locker that holds tight enough to keep them in place for the job. But can be removed with the same tool(s) you put them in place with originally and with no damage to the screw or surrounding metal.
Wether it's NailPolish, one of the LocTite formulas or a specialty compound made for this,, just don't permanetly seize them into place.
