Loctite Blue is way too strong for gun screws. According to Loctite, Purple 222 is used on screws up to size M14 (1/2" +,-) while Blue 243 is used on threads M14 up to M20
which is way too strong for finely threaded gun screws. This link http://tinyurl.com/pqts2tb will get you a pdf from Loctite on which threadlocker to use where and how to use it.