Use what you personally have positive experience with, if it works for you, thats what you need. It wouldnt matter if its Loctite, paint pen, nail polish, Elmers glue, dried snot, or anything else, if it works, it works. The thing people dont do much these days is test things for themselves, they listen to too dam many self proclaimed experts. Years ago thats what we all did, we worked on it and made a decision. We are talking base and ring screws here for the most part, not the jesus nut on a helicopter.
I have used a whole lot of Loctite products over the last 35 years with success. Some of it was in the tool cabinets on my truck in 108 degree summers and in it during freezing weather as well, no failures. I have had it ruin if it was old, you kind of know it is bad if you have used it enough. Retaining bearing races and sleeves with green, locking threads with blue and red were a daily thing. This is all on heavy earth moving, mining, and oilfield equipment here in the US, UAE, Algeria, North Sea, Mexico and Russia. Large bolts are no issue, smaller bolts and screws need care to not over apply. We use 4-40 screws a lot in our electronic panels to hold circuit boards and other items. They are subjected to impact, high and low frequency vibration, and other forces that will rattle things apart, Loctite has always worked, using nothing has never worked here. I cant imagine the recoil on a rifle is any worse.
When it comes to rifles, I have used Loctite and nail polish, and have had success with both, as well as using nothing at all, I have never tried a paint pen. I use good torque instruments,( not the cheap 60.00 trash), we can calibrate them daily if we wish. Torque is of the most importance, and like shooting, there is a feel to it, and you have to drive the instrument properly. Installing a fastener is a process, although it is a simple one in most cases, it is still process with all steps needing to be done properly. Thats where I believe most have failures, the devil is in the details.
Rambling is over now!
