How Does Oil Actually Lubricate?

It may seem like a silly question, but how does oil actually work as a lubricant?

Oil overcomes friction between moving parts, we all know that. But how?

At a microscopic level the parts in your gun are very rough (think of jagged mountain peaks, when viewed under a microscope). So if one where to rub those surfaces against each other, the jagged peaks of each part, get stuck on each other. The harder you push the parts together, the more they stick, and the more lateral force is needed to make them move relative to each other. This is essentially what friction is.

Obviously the smoother you can make the parts, the less jagged they will be at a microscopic level, which helps them slide past each other. Which is why some critical moving parts might be highly polished – but this only partially solves the problem, at a microscopic level, you can never make the parts absolutely smooth.

What oil does is fill up the space between the two moving parts with a liquid, and if the oil has a high enough viscosity (we will discuss viscosity later), so that the oil is not forced out of that gap between the parts as they are pushed together, then those two parts do not come into contact with each other, and instead “float” on a film of fluid, and thus can move much more easily relative to each other. This reduces friction, as well as reduces part wear significantly.


Viscosity is essentially a measure of how “runny” the oil is, at different temperatures.

We all know that treacle syrup can be very thick and difficult to stir when it’s cold, but if you heat it up, then it becomes nice and runny.

Oil behaves the same, it gets more runny, as it gets hotter. Viscosity defines how difficult the oil is to stir, or flow, as it were. The higher the number, the thicker the oil, at the specific testing temperature. It’s a bit more complicated than that, but that’s all you need to know, without an engineering degree.

We are all familiar with multigrade motor oil which has two viscosity ratings (eg 15W 40). What those two numbers mean is that when it is cold, the oil behaves as if it has a viscosity rating of 15, but once the oil heats up, it behaves as if has a rating of 40. So multigrade oils behave as if they are a thin oil at low temperatures, and then change to become thicker at higher temperatures, in comparison to traditional single grade oils. Note the “W” designates a rating from a standardised cold temperature test, while the other number is a rating for a high temperature test, so strictly speaking, those two numbers cannot be compared to each other directly. What that essentially tells you is how “thick” the oil will be when it’s cold, and then how “runny” it will become when the engine reaches operating temperatures. So another oil with a rating of 0W 40, would be more “runny” at the colder testing temperatures, but the same at the higher operating temperatures. From a user’s point of view, one does not want the oil to be too thick at low temperatures, but not too runny at higher temperatures.

This property of viscosity is extremely important, because it defines how much load the fluid film can carry, before it is forced out between the parts, and thus allowing damaging metal-on-metal contact.

Thus it’s important that you select an oil with the correct viscosity for any lubricating task. If the oil is too thick, it will be like trying to stir treacle and the parts won’t move easily, if it’s too thin, the oil is just going to be forced out of the gap between the moving parts and thus there will be nothing stopping the parts from making contact with each other. The objective is to get the parts to float on a film of oil, and thus allow the parts to glide smoothly relative to each other.

Environmental Factors

Temperature is major factor.

If you happen to operate in artic conditions, your choice of oil might be very different to someone operating in the tropics, due to how temperature has a large effect on the viscosity of the oil. Colder climates are going to be more of a problem, because the range of operating temperatures your firearm has to work in, is going to be much larger. The issue is how the oil performs during your first few shots in very cold weather, while everything is still cold, or if you shoot with long pauses between shots, so that the gun parts remain relatively cold. In those circumstances, the oil should not get too thick at those cold temperatures, which may slow down the moving parts too much, to the point that the gun does not function reliably.

Another factor in cold weather is ice forming within the working parts and thus preventing the gun from operating by locking the mechanism solid. A layer of suitable oil, which repels water and condensation, might keep crucial surfaces free from ice formation, if that becomes a problem.

If your environment is very dusty, that can also be a major factor. Fine talcum type dust can be very difficult to deal with, because it tends to penetrate right into the working parts, coating everything in a horrible layer of abrasive micro-particles. This is made worse by those dust particles becoming stuck to oil coated surfaces, and thus forming a nasty grinding paste, potentially jamming everything up, as well as causing rapid wear.

Sea spray and mist is very corrosive. This is worse in costal areas which have high humidity, where things do not dry easily. If you operate in, on, or near the sea, that will no doubt include it’s own challenges when it comes to firearm lubrication. Oils that repel water and are not affected by salt will probably be important, which are not covered in this article.

Firearm Reliability Design, and Lubrication

Because reliability is probably the most important attribute of any defensive, or military firearm (when it’s needed, it’s probably a life-or-death situation, so it better work), and because firearms are often used in very harsh operating environments, a lot of design effort is usually spent on finding the range of tolerances, materials, surface hardnesses etc, which result in a weapon that works under literally any conditions.

Crucially, those operating conditions can include inadequate, or even zero, lubrication.

The famous example of this is the AK47 rifle.

The Glock range of pistols also have a similar reputation.

However, just because a machine will operate without lubrication, does not mean one should do that as a policy, unless one has to.

Also, not all firearms are reliable enough to operate without cleaning and lubrication. Some weapons are high precision instruments, with very tight tolerances, which may require frequent cleaning and lubrication.

In general, any machine will work better, be more reliable, more precise, and last longer, if it is properly lubricated. Just something to keep in mind. The same goes for firearms.

Too Much Oil Can be as Bad as Too Little

In very dusty environments particularly, too much oil, can cause jamming and damage, due to the fine dust particles becoming stuck and accumulating on oiled surfaces and thus clogging up the works, or being absorbed into the oil to form a grinding paste.

In those conditions, it may be better to only use the absolute minimum amount of oil necessary. Make sure then that there is no oil coating any surface on the weapon where oil is not needed, to avoid dust particles become stuck to those surfaces and accumulating there.

In addition, where parts have to reciprocate rapidly inside narrow enclosed channels, trapped oil can slow down, or even stop, those parts from moving, due to viscous drag, or hydrostatic pressure. So in those situations, if the weapon was not designed to have oil in those channels, then one should not allow oil to get into those spaces.

So with most firearms, it is usually quite important exactly where you put your oil, and how much you add. You should only oil a few specific surfaces, as per the manufacturer’s instructions. And those surfaces should not be dripping with oil. The minimum amount necessary is the rule. Less is more, as it were.

The good news here is that it only takes a very small amount of oil to properly lubricate most modern firearms. A few drops, is all you need in most cases.

This issue will be more pronounced on high precision weapons, with fine tolerances.

Applying Lubricant to Gun Parts

As was pointed out above, one of the key things about lubricating firearms is getting just the right amount of oil onto precisely the right surfaces.

This is very different to what is happening inside your car engine, for example. A car engine usually has an oil pump, which pumps the oil through tubes and channels within the engine. So all relevant contact surfaces have a continuously replaced film of oil pumped to those surfaces. The oil is pumped at quite high pressure, directly into the gaps between those parts, which also ensures that the parts do not come into direct contact with each other, more than they should.

But no such oil pump exists within most firearms. So you have to put the oil onto the surfaces you want to be lubricated yourself, and it has to stay there while you operate the firearm. The oil should not seep, or run into spaces, where it should not be, even as the weapon heats up as you fire it, nor be flung off by rapid acceleration of the parts, as they reciprocate during the firing cycle.

Also, as was pointed out above, ideally, one wants to only apply the correct amount of oil to each surface.

So how best to achieve that task?

Surprisingly, while the best solution is fairly straight forward, I have not seen it suggested anywhere else.

Some gun oil manufacturer’s will supply their oil in containers that include a long thin metal tube, which does help to some extent, to get drops onto the right parts. But those containers are not readily available, certainly not from South African gun shops.

But, in any event, a better solution is cheaply and readily available. Just go to your local craft store and buy a very fine, thin paint brush. The sort an artist would use for very fine, thin dainty strokes on a painting. The smaller, the better. Typically the bristles are a bit too long, so cut them down to about 5 millimetres with a sharp scissors. When you think about it, a very thin paint brush is exactly the right tool, because it is used to apply just the right amount of paint, in a very thin line to a painting. You can do exactly the same thing, using it to apply oil to exactly the right parts of your gun, while carefully controlling exactly how much oil is applied, far more precisely than you could with some sort of tube or drop applicator. You can also get into some very small and difficult to reach spots with such a paint brush. Just think, could you paint a reasonably high resolution painting, by trying to drop drops of paint onto the canvas, from the drop applicator supplied by some gun oil suppliers? A small thin paint brush is much easier to use and is far more precise. So perhaps try that out, see if it works for you?

What Oil to Use?

This question is one of those hotly debated topics, similar to the favourite recipe for some home cooked special meal, which has been handed down in the family through the generations, grandfather to father, father to son. Where many people will have very different, but very firm opinions on the subject.

Here are mine.

The same debate occurs with motor vehicles and larger heavy machinery, about what oil to use. Although in those cases, there are some significant differences to the context of the debate. A high performance motor engine can rev up to speeds of 10,000 revolutions per minute. And can last for 20,000 km, or more, without needing an oil replacement. In addition, if a company is running a fleet of heavy duty trucks, they will track the operating costs of that fleet in very great detail, and have their oil analysed by specialised laboratories to track wear rates, friction, fuel efficiency as related to engine oil performance etc.

Generally, the answer to the debate of what oil to use to use in any motor vehicle, is whatever the manufacturer tells you to use. What your grandfather thought about the subject is no longer relevant, when it comes to modern day engines and advanced lubrication technologies.

Most firearms, in comparison, do not cycle anywhere near as fast, or for as long, as motor vehicle engines, especially when it comes to the context of civilian use. So, unless you happen to own a Phalanx Mini Gun, the average citizen’s firearm will probably cycle less times over its entire life, than the average motor vehicle engine cycles in a minute or two of hard running.

You can probably see where my logic is going.

I think a great oil to use in any firearm, is any high performance diesel engine oil, specifically for these reasons:

  • Gun oil is sold in small containers that can be quite expensive per container, when compared to engine oil. If you just fill a small container with some new engine oil, the next time you top up your vehicle’s engine oil, that will cost much less than a similar container of gun oil, and in fact is essentially free, if you use the rest of that oil for your vehicle.
  • I believe the lubrication technology employed within modern engine oils is at very a high level, much higher than available gun oils. For example, oil designed for diesel engines includes detergents that break down and absorb soot deposits, without adversely affecting the lubricating properties of the oil. Firing guns generates similar soot deposits on the working parts. Another example is multigrade technology which makes the oil perform better in freezing temperatures. One could go on. The fact is it’s very difficult to find any performance specifications and standards for gun oils, in general. Which implies perhaps that none are adhered to, or developed?
  • The slightly higher viscosity of engine oil (depending on what viscosity grade you choose – I use 15W 40), in comparison to some gun oils, seems to help the oil stay where you put it, without seeping or running away, or getting flung off, even when the weapon’s parts are reciprocating rapidly. So this helps keep the oil only where it is needed.
  • The operating temperature ranges of firearm parts is about the same, as what is happening inside most engines. The relative speeds of the moving parts are also high in both cases.

Those are the main reasons why I think high performance diesel engine oil is a good choice.

But ultimately, which oil to use is probably not a very important debate. Simply because many modern firearms are very reliable, and operate well regardless of your choice of oil. Some are even known to remain reliable without much, or any, cleaning and lubrication at all. So one can quite validly ask, does it really matter what oil you use? I would think that it probably doesn’t really matter that much for many people. So if you really want to use what your grandfather always used, then go ahead, that will probably work just fine!

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