There’s so many different types. Blue is medium strength and it should be metal on metal? 
the type of loctite you use is entirely dependent on what you’re loctiting… ?
use RED for permanent fastening… blue is for non-permanent thread locking. use red for things like gas keys… blue for things like pistol grips.
i rarely use loctite, myself… tightening and staking generally takes care of whatever you’re doing
Well, for optic mounts. I’ve been told to use loctite so that the vibration doesn’t eventually cause your sight to be off.
thats good advise. use blue for that.
Yes, use blue for that. It works quite well and is widely used on the screws for all sorts of mounts and accessories.
As mentioned above, use red for stuff you NEVER plan on removing. The red is technically removable, but it can be a real bitch.
Derek
I use the red for almost everything and have no problems getting it loose when needed. Just use a small amount.
…are you then recommending people do this?
Just make sure what you are using for what purpose. Blue loctite is medium strength and sufficient for most things. Red is super heavy duty and only for things you don’t plan to take off for years, if ever. There is also a very handy green wicking loctite for assembled threads (that can migrate in interesting ways–be careful). And if you think the tube always indicates the color of the stuff inside–it doesn’t. So read the label and double check the contents and its number if you’re not sure.
Red is a bear to get loose, and moderate heat is almost a must. Some time ago I got an ACOG with the TA60 base mounted to it and red loctite on the screw. I had to remove the factory base to mount the optic. Why the hell Trijicon used red I will never know. I wound up playing the flame of a hand torch on the screw head (VERY carefully!). Doing that on a $900 optic is a nervous undertaking to put it mildly. But the point is, it works.
Used properly, loctite in its many forms is great stuff and I use it regularly. Just proceed carefully.
What about the pre-applied thread lockers that cure when crushed thread to thread. Anyone know a source for this?
I like it because it’s less messy than lock-tite, I find it on medical equipment fasteners all the time but haven’t found a good source on the net yet.
Components assembled with Red loctite (262) can only be correctly disassembled when heated to around 500f. Sometimes you get lucky, but sometimes you take the threads with the fastener, especially when you have dissimiliar metals such as a steel fastener threaded into aluminum. Most applications on weapons would be Blue loctite (242) which is designed for frequently assembled and disassembled parts. Personally, I would never use 262 on optics or anything other than the gas key screws, and I’m in agreement with bkb0000 that staking is the proper restraint for that application. The only warning with 242 is it not compatible with some thermoplastics.
I recently came across a less messy loc-tite product (blue - medium strength) that may work for you. It comes in a tube just a bit larger than your typical lip balm, and it’s waxy, so it doesn’t run all over the place. One tube lasts a loooong time because very little is wasted. Here’s a link to amazon, but I think I found mine at Home Depot or Lowe’s:
http://www.amazon.com/Loctite-LOCTITE-MD-STRNGTH-Chemical-Threadlocker/dp/B0002JMLPQ
Don’t forget, for some smaller applications there’s Loctite 222. It is purple and designed for smaller screws 1/4" and less, might be just right for things like optics screws. The only warning is like 242, it may not be compatible with some thermoplastics. I use this all the time for small screws like hand controls, covers etc. on my Harley and never have problems with vibration loosening.
I can’t think of many things on a firearm that I would use red for, certainly not optics.
Blue is a happy medium.
I’ve used red before and messed up screw heads getting them out. Blue seems to work for almost everything and I’ve personally never had it come loose.
With Loctite, a little goes a long way. A common mistake is to use too much. A small drop of the blue should work just fine.