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http://www.armalite.com/images/Tech Notes/Tech Note 62 Lubrication of Firearms 100726 Rev 1.pdf
just one of many........it gets hot. go ahead touch it. If your thinking other modes of lube try some synthetic brake grease with teflon or even graphite.
I follow the general guide lines from my owners manual.
FWIW, I take a patch or two, hold them over the opening of a bottle of Mobil 1, soak the patch and use that to coat all surfaces of the bolt carrier group (except for the face itself) with a fairly heavy coat of oil. This includes the bolt, carrier and cam pin. I also coat the internal portion of the charging handle. For the trigger group, I like this stuff:
It foams which helps get into smaller parts.
You don't need to coat the whole BCG. You really want to just look for the metal that rubs on metal parts. Usually only four little "rails" on the BCG that need to be lubed. Anything else is just going to attract dust/dirt.
I have used militech1 lubricant on all my M-4's in the military, and at home for the past 6 years. Both in Iraq and Afghanistan, my weapon has never jamed on me ever. I lube the friction points on the bolt, light coat where the gas rings are, and MOST important, I take some lube make a small puddle in my hand and coat the buffer spring real good. I have seen many guys not lube there buffer spring, and the spring ends up causing so much friction in the tube, it has trouble not having enough ummph to strip a round off the mag when firing.
+1. I use 20wt synthetic on my centerfire guns and 0 or 5wt on the rimfires. I'm not real picky as to the brand, I use whatever is left over from the oil changes in the truck and motorcycle.
For you purists out there, there isn't a lot of real synthetic on the market. The only two I can think of offhand are Amsoil and Royal Purple, but I'm sure there are others. The major manufacturers like Mobil and Castrol are selling blends as pure synthetics.
Got a cite on that?
I know Mobil 1 has started selling some with that branding that are really blends. Other types of Mobil 1 are still supposed to be full synthetic.
For a gun though, I really doubt it matters. The abuse motor oil gets in an engine is far worse.