If you really don't want medium to large sized bolts to come loose, I'm talking m4 and up, Loctite 263 has been my choice. If used sparingly it usually doesn't require heat, but on smaller bolts it's a good idea to use a little heat to keep from stripping the heads.
For scope bases and internal screws that will be exposed to oil and solvents, 243 is my goto. No heat required, but a little contact with a solder iron doesn't hurt to make things easier.
For scope bases and internal screws that will be exposed to oil and solvents, 243 is my goto. No heat required, but a little contact with a solder iron doesn't hurt to make things easier.