I was taught to use oil if it rotates and greaseif it slides - with a couple common sense caveats.
Grease first.
On a semi auto like an M1, M1A, BM-59, M1 Carbine, Mini-14, etc there are specific points that call for grease. And most of those points have shiny spots on them. On those above rifles, it’s:
- the roller on the bolt;
- the recess for that lug or roller in the slide;
- the square retainer lug on the back of the slide;
- that shiny spot on the back of the bolt where it contacts the top of the receiver;
- the shiny spot on the bottom of the op rod where it contacts the bottom of the barrel; and
The shiny curved section of the hammer.
But you don’t have to remember that because if it’s shiny it gets a light coat of grease.
As noted above no manufacturer seems to recommend grease on slide rails. However, pistols like the 1911 like to run wet and pistols with aluminum allow frames absolutely need to run wet to keep the steel slide from excessively wearing the aluminum frame rail.
That leaves you with the option of using a sufficient amount of oil to keep the rails wet, and if it’s not slinging oil at you when it cycles the first few times it probably isn’t enough.
However, you also have the option of using a thin coat of grease. Here in the south, grease is my go to lubricant for frame and slide rails, the locking lug detents, and a light shine of grease on the guide rod. That gives me long lasting, non dripping, holster and concealed carry friendly lubrication.
This is where some common sense is required. I live in the south now, but grew up in the frozen north and spent about half my adult years there. When it’s -20 F, grease can be a problem. So can many higher viscosity oils. That’s one of the few places and times where I think CLP is a good choice. Rem oil isn’t bad either given it’s low viscosity. Even here on NC when it gets down near freezing in the winter, lightly grease slide rails can start to cause malfunctions in some pistols as slide velocity is reduced.
Even on a bolt action rifle, if I was going to grab a white sheet and go out on skis to hunt coyotes, I disassembled the bolt, cleaned all the grease and oil off it and the firing pin, and then very lightly oiled it with CLP, and only used a very thin coat of grease on the bolt cocking/camming surfaces. I’d usually do that at the onset of winter and call it good.
Too much grease is also a bad idea as it can hold onto any grit it comes in contact with.
What kind of grease? There’s nothing wrong with Tetra or Rig.
Mil-spec rifle grease is fine, but it’s not “better” just because it’s mil-spec. At the time that specification was adopted the primary consideration was resistance to washing off. Any lithium grease you find at the local auto parts store will exceed that specification and they will all provide equal or better lubrication.
That said I use military rifle grease as I bought a few cans way back in the day when they were dirt cheap and that supply will outlast me.
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Now let’s talk about oil.
For general lubrication I like Rem Oil. It’s thin, gets where it needs to be and doesn’t gunk up if it gets where it shouldn’t be, and offers a reasonable degree of rust protection.
I’m not a CLP fan as it’s pretty volatile (it’s a cleaner as well) and once it dries down, it offers very little protection. I generally regard CLP as declining in performance in that same letter order.
In the military I landed squarely between wars and in the transition from the M16A1 to the M16A2, the 1911A1 to the M9, and from LSA to CLP. All of those were in my opinion moves in the wrong direction.
CLP worked only because we put it on regularly and pretty liberally. There were folks later on who advocated running the M16 almost dry as oil would attract grit. It was a nice thought, but the M16/M4 likes to run wet. You just need to pop the rear pin, pull the bolt, wipe it and the inside of the upper receiver and then relube it - every time you get the chance and or get sand in it.
For long term rust protection neither CLP nor Rem oil works all that well as both dry out and don’t leave much of a protective film. Hoppes Gun Oil on the other hand does fine, even here in hot and humid eastern NC. It leaves a good protective coat that will last for several months. Try not to get too much in the internal parts of the gun however.
For my concealed carry handguns, I’ll lube the internals with rem oil and then wipe down the outer surfaces with a patch with Hoppes Gun oil on it.
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Please note that Hoppes Gun Oil and Hoppes No. 9 are not the same product. Hoppes No 9 is a powder and copper solvent and provides absolutely no rust protection once it dries out. In fact it usually removes any oil and grease as well and acts as a degreasing agent in the long term.