Lubrication 101: Gun oil, snake oil, and how to tell the difference.

Introduction

Firearms enthusiasts are the targets (pardon the pun) of some of the most misleading advertisements regarding the proper lubrication of their guns. The purpose of this article is to give a background on basic lubrication concepts, the technology behind them, and some guidelines for selecting lubricants based on facts, not hype.
Before going further, let’s make something perfectly clear: with a very few obvious exceptions, firearms lubrication isn’t terribly difficult. Compared to many more common objects, guns just don’t make big demands of their lubricants! That’s right, firearms pose no actual “extreme” situations with which a lubricant must deal. There are thousands upon thousands of 100-year-old-plus guns out there that are functioning – just fine, thank you – on a diet of “3-in-1” oil.
However, that doesn’t mean that there isn’t something better. This article, it is hoped, will help you determine just what “better” means to you.
(Over the years I’ve been honored to have a number of tribologists — the technical term for oil engineers — contribute and correct this article. I thank each and every one of them for helping me to keep this as factual and current as I can!)
 

Let’s start at the beginning…

Why lubricate something? First, to prevent wear and second, to promote a certain level of performance. To put it more clearly, what we’re trying to do is to keep parts from rubbing directly on other parts, and to make the interaction of those parts as smooth as possible.
As it turns out, those polished surfaces that rub against each other aren’t all that smooth. Looking through a microscope, even the most highly finished metal surface still looks like a forested hillside – with all kinds of huge voids, depressions, and valleys. Imagine, then, what happens when that surface meets the surface of it’s companion part! Not only does the combination become difficult to move, but the tops of those trees get broken off – that’s how wear starts at the microscopic level.
That’s why we lubricate those surfaces. Lubrication works in a couple of ways: “hydrodynamic” and “boundary”.
Hydrodynamic lubrication is essentially when the parts ride on the film of liquid (or semi-liquid) lubricant; the lubricant fills all of the voids, and the film itself serves as a buffer to keep the surfaces apart.
This works really well, except when a load is applied and the lubricant is squeezed out of its space between the surfaces. When that happens, the surfaces grind together and wear. What if we added something to the mix – something that was a bit more “solid” than the lubricant, which wouldn’t be easily squeezed out? Well, that’s just what “boundary” lubrication entails – adding small pieces of more-solid material to serve as a physical separator between the surfaces, keeping them from tearing each other to pieces.
The solids that provide this service are known as “anti-wear” or “extreme pressure” (AW/EP) additives – solids of microscopic size that are mixed into a lubricant, in order to maintain a protective boundary (get it?) under load. “Moly”, a generic term for several molydenum compounds, is one example; others include sulphur compunds, zinc, polytetrafluoroethylene (PTFE, aka ‘teflon’), zinc diakyl dithiophosphate (ZDDP), phosphors, boron, antimony diakyl dithiocarbamate (and its derivatives), and many more. Each of these has certain properties that the skilled tribologist (lubrication scientist) will balance to achieve the optimum lubricant for the application.
Regardless of the physical characteristics of the product, lubricants are a “package” – the primary lubricant plus boundary additives, thickeners (as in greases), and other things (tackifiers, pour point depressants, detergents…the list is endless and chock full of chemical names I can’t begin to decipher!)
My exaggerated interpretation of the primary lubrication states:

 

All about grease

Grease is nothing more than thickened oil. Grease is made by mixing oil with a “base” to thicken it – the base being a metallic soap (lithium, aluminum, barium, calcium), or a non-soap alternative (bentone, polyurea.) Each of these bases have different characteristics, which are taken into account (along with the oils and additives) to produce a grease of the desired effectiveness.
Different bases will show different degrees of water resistance, cold weather performance, stability (the ability to resist oil separation under shear and mechanical operations), oxidation, and “reversability” – the ability of the base to re-absorb any oil that might have been separated out.
Lithium is the most common base encountered; it’s cheap, easily produced, and has enough good traits to make it a decent choice for general purposes. Aluminum bases, though, have several advantages: much better resistance to water (and acids and alkalis), better low-temperature performance, better stability, and dramatically increased reversability. Aluminum greases are typically a bit harder to find, and more costly, but their performance advantages can be pretty dramatic.
Grease is graded in thickness by its NLGI number. Most grease you’re familiar with is NLGI #2; smaller numbers mean less thick, larger numbers mean thicker. A grease rated at NLGI #00 is almost a liquid a room temperature.
 

What makes for a good gun lube?

Believe it or not, and contrary to what a lot of marketing hype will try to tell you, firearms aren’t generally all that hard on lubricants. They encounter intermittent high loads, interspersed with long periods of inaction. This means that the primary lubrication need isn’t hydrodynamic – it’s boundary. What, then, should we be looking for?
Start with a very good boundary lubrication package – that translates to lots of EP/AW additives. We need superb corrosion resistance, along with resistance to oxidation (don’t want those lubricants thickening up during non-use.) We could also use some water resistance and an ability to withstand mild acid and alkali exposure (think perspiration.) Low temperature performance would be icing on the cake, and for a grease we want something that won’t easily separate under load.
We need our oils to migrate. No, I don’t mean to fly south for the winter! Migration is the ability of the lubricant to spread to surrounding and adjacent areas. For instance, let’s say we’re lubricating the shaft on which a hammer pivots; a lubricant with poor migration would just sit where we applied it, and would never get into the space between the hammer hole and the pivot. The net result would be a poorly lubed mechanism. A lube with good migration will succumb to capillary action and snake its way down into that small space, lubricating everything it comes into contact with.
Sounds like migration is just the cat’s meow, right? Not really – there is such a thing as too much. The migration that is so desirable on hammers and triggers isn’t really good on autopistol slides; the lubricant tends to “run off”, or migrates to the holster (or your clothes.) Ever wonder why your autoloader slide goes “dry” while in the holster? Lubricant migration at work. (What, you think it disappeared into thin air?)
What about greases – do we even need them? You bet! I use the General Rule of Lubrication: oil for rotating parts, grease for sliding parts that carry a load. In firearms, grease is most appropriate for any part interaction that has a scraping (aka “shear”) type of action, and will be subjected to pressure or shock. What kinds of parts are we talking about? Slide rails, bolt carriers, and sears – especially double-action sears. (An example of a sliding part that should not be greased is the trigger bow of the 1911 pistol – it carries virtually no load, and is subject to almost no stress; it also is under very light tension, so little that a thickened lubricant could reduce its free movement.)
That’s a pretty good explanation of what we need – is there anything we should avoid? Of course – any product that contains chlorine compounds. These compounds, usually referred to as chlorinated esters, were used as boundary additives for many years. As boundary lubes they actually work pretty well; the problem is that they promote a phenomenon known as “stress corrosion cracking” (SCC). Essentially, SCC creates microscopic pits and cracks that, under heat and pressure, widen to become noticeable cracks – and sometimes, even broken parts!
(One major gun manufacturer actually had barrels fall off of their revolvers. An investigation ensued, and they found that the chlorinated esters used in their machining oils was causing stress cracking in barrel threads. When combined with the gun owners’ use of cleaning and lube compounds containing chlorinated esters, the barrels simply sheared off at the weakest part – the threads. Like most aircraft makers, the company learned to forbid chlorine-carrying compounds on the manufacturing floor, to prevent a recurrence.)
 

What about “miracle products”?

Let’s be clear: there are no “new”, “revolutionary” lubricant products made for firearms. That’s a flat statement, and it’s intended to be. All of the lubricants, bases, and additives of suitable use are already well known to the lubricant industry. Specific combinations might be unique, but it’s all been tried before – if not necessarily on guns.
There are several such products on the market right now that are simply a well-known boundary additive in a light carrier; at least one of them is a chlorinated ester! These things have been around a long time, and unless you didn’t know better the products using them would indeed seem to be “revolutionary.” Just remember: any new gun lube is going to be made up of readily available components, perhaps blended especially for the requirement, but will not be a “miracle”.
 

Cut to the chase! What should I use?

Let’s start with oil. Most people use oils that are way too heavy; thicker is not better! Use a relatively thin oil with the correct properties, and use it very sparingly – most “oil failures” I’ve seen have been from too much, rather than too little, oil.
Frankly, in terms of mechanical performance, most oils “work”; some are better than others, but everything will make parts move for a while. The weakest area of most oils is in corrosion resistance – and on a gun, corrosion is a bad thing! There have been lots of claims, but those people who have actually taken the time to run experiments to test corrosion on steel have found that the products with the greatest hype are often the worst at corrosion resistance. Not surprisingly, plain mineral oils, such as Rem Oil, score at the very bottom of the list. (To that you can usually add most of the plant- or vegetable-based oils.)
In years past I recommended Dexron-type Automatic Transmission Fluid (ATF). That’s right, plain ol’ ATF. The kind you get at every gas station, auto parts store, and even most convenience stores. It does pretty well in corrosion resistance (not great, but better than average.) It also has good migration, a fair boundary lubrication package, is the right weight (thickness) for general firearms use, doesn’t oxidize over long periods of storage, and is compatible with a wide range of metals and plastics. Synthetic or regular, either will work just fine.
ATF is not perfect, however; aside from the aforementioned deficiencies, it does have a slight odor to it, the red dye used to differentiate it from motor oil will stain, and it’s not non-toxic. Particularly because of the toxicity I no longer recommend its use. (A decent alternative that is still readily available is “NyOil.” Check your local auto parts store, in the aisle where they keep the miscellaneous lubricants and additives.)
What would I consider a “best in class” oil? Generally, it would be one made for lubricating food processing machinery, like Lubriplate’s FMO-AW oil (specifically the 350-AW weight.) Food grade lubricants have to prevent wear in sometimes corrosive environments and they have to do so even after being wiped off of the surface they’re protecting (which is actually part of the requirement for food contact ratings!) They have good boundary protection and very high corrosion resistance especially in the presence of acids, alkalis, and moisture. They’re darned near tailor-made for our use!
I’m aware of at least one large coastal police agency using Lubriplate FMO-AW, and they report complete satisfaction with its performance. Unfortunately, it’s not (as of this writing) packaged in consumer friendly quantities – 1 gallon pails being the smallest available. You can get it repackaged in consumer sizes from Lubrikit *.
 

What about grease?

Remember that you should grease sliding parts that carry a load – slide rails, sears, and bolt carriers. Again, remember to start with your criteria: must have superb boundary lubricants (particularly when used on double-action mechanisms), good cold working characteristics, resistant to acids/alkalis and water (especially water), and preferably of a non-staining variety (black grease stains look awful on clothing!)
Many people use Brownell’s Action Lube as a popular general purpose grease – it has wonderful boundary lubricants (in fact, it is mostly composed of molybdenum compounds in a light grease base) and great shear resistance. It is superb on action parts, and works fairly well on slide rails – as long as you don’t mind black stains. Yuck! It does exhibit poor oxidation characteristics and reversibility; though I have no hard data, I suspect it also doesn’t resist water or pH changes all that well. For internal parts, which are protected by housings, it is terrific and gives actions a unique ‘buttery’ feel. I use a lot of it to lubricate sears and rebound slides, but for all other needs there is a much better choice.
Again, food machinery greases are ideal for our needs. For such things as autoloader slides and rifle bolts, my favorite is Lubriplate “SFL” NLGI #0 grease (their “FGL” line is a good second choice.) In my testing it’s proven itself superior as a general lubricant. It is white, aluminum-based, low odor, has superb boundary lubricants, and is designed specifically for use in environments that encounter a huge temperature range. It’s also resistant to water washout and acid/alkali environments, has great shear resistance, and doesn’t oxidize like lithium greases will. As an all-around grease I’ve found nothing better. It’s available from www.lubriplate.com, in their online store. It comes in a 14oz can which will last you for years – no matter how many guns you have! (Again, Lubrikit has it in smaller sizes.)
(Lubriplate also makes SFL in heavier grades, such as NLGI #1. While thicker than the #0, it is still a pretty light grease, and would be my recommendation for very hot climates. The NLGI #0 is a better choice for most of the United States.)
 

But what about……?

Everyone has their own little “secret”. If it works, is there anything wrong with it? Let’s find out…
Motor oils: Generally good boundary lubrication (particularly the Havoline formulations), but very poor corrosion resistance and poor resistance to open-air oxidation. The biggest problem is that their pour-point additives often contain benzene compounds, which aren’t a good thing to have next to your skin on a regular basis! I recommend staying away from motor oils; if you must use something from the auto parts store, ATF performs better for firearms use on every count, even if it is a tad more expensive. (ATF is still 1/10 to 1/100th the cost of a specialty “gun oil.”)
Gear oils: Too thick for the application. In addition, they contain tackifiers which gives them poor migration and lead to oxidization in open air, rendering them even more “sticky” – pretty much what we don’t want. (Some folks use it on their slide rails because it’s thicker and won’t migrate easily; a light grease is a far better choice.) If you really want a thicker oil with all the good characteristics we’ve covered, but is still cheap, mix ATF and STP Oil Treatment in a 40/60 ratio. Far better than gear oil on every count – but I’d still much rather have a good food grade NLGI #0 grease.
WD-40: WD-40 was never meant to be a lubricant – it was designed as a moisture displacer. It’s far too light for any load protection, has incredibly poor corrosion resistance, contains zero boundary lubricants, and rapidly oxidizes to form a sickly yellow varnish (hint: this is not good for delicate internal lockwork.) There are those who will defend this stuff vehemently, but then again you can still find people who think smokeless powder is a passing fad. Just. Don’t.
Automotive motor oil additives: Usually a boundary additive in some sort of light mineral oil carrier, they usually lack corrosion protection and often oxidize rapidly; some have poor migration characteristics and rely on the oil to which they’ll be added to provide those things. When mixed with an appropriate oil (such as ATF) these additives do have some merit (see above), but by themselves? No.
Silicone spray: Right up there with WD-40, but at least it’ll shed water while your parts grind themselves into little shavings!
Graphite: (sprays, powders) Graphite is a crystalline product which is actually very slightly abrasive. It offers no appreciable benefit other than being dry; a lube with a good boundary lubricant package can be wiped dry to the touch and still provide better lubrication and protection than graphite. Save it for your keys and padlocks.
Finally, note that the foregoing is a layman’s understanding of lubrication technology. I don’t pretend to be an expert, just a well-informed amateur hoping to disseminate some arcane knowledge. I have had the support, input, and feedback of a number of specialists and experts in the lubrication industry who have vetted what I say, but as always: use at your own risk!
– Grant
* – I have no affiliation with Lubriplate or Lubrikit other than as a customer, and I do not receive nor have I asked for any sort of consideration or discount for recommending their products.