There are advantages and disadvantages to every type of lubricant. This discussion is intended to give a layman’s introduction to the most common types of wet and dry lubricants and the strengths and weakness of each.
Lubricants reduce friction by creating a layer of material that separates two surfaces that are rubbing together. This means that the lubricant functions by actually preventing two surfaces of the machine from touching.
To give an example, imagine taking two sheets of metal and putting a handful of ball bearing between them. The two layers of sheet-metal do not actually touch each other. The ball bearings are acting as a dry (solid) lubricant between the metal plates.
Now consider doing the same thing with a semi-solid lubricant such as grease. Take one sheet of metal then cover the top of it with a layer of grease. Then take another sheet of metal and place it on top of the grease to create a sandwich. The grease would keep the metal plates from touching. Even if the plates are pressed together and most of the grease is squeezed out, there will be a thin layer that remains which will keep the plates from actually contacting each other.
The same is also true if you use a liquid lubricant such as motor oil. The top plate would be separated from the bottom plate by a thin layer of oil. However, the amount of separation gets smaller and smaller as you use lighter weight (thinner) oil. The amount of separation also gets smaller as you put more pressure on the top plate.
Common dry lubricants are graphite, molybdenum disulfide and PTFE. Graphite is a special type of carbon that works quite well to reduce friction and wear. One thing to be aware of with graphite is that it can cause corrosion in many types of metals including steel and aluminum. Molybdenum disulfide is an excellent material that works under a very wide range of temperatures and pressures. Moly also does a good job of staying in place. However, a downside is that after contact with water moly can form acids that will damage a firearm. The last on the list is PTFE which you may know by the trade name Teflon. PTFE does a very good job as a lubricant, but it doesn’t have as wide of a range of operating temperatures as the other materials.
Liquid lubricants are most commonly petroleum (mineral) based oils. They can be produced by distillation from crude oil or similar products can be produced synthetically. These lubricants are typically blended with a variety of additives to improve the performance of the raw oil. Liquid lubricants tend to be fairly effective at keeping abrasive particles in suspension and distributing heat. These are the same basic oils that are used in your car.
Semi-solid lubricants are simply various types of grease. One advantage of grease is that it tends to stay where it is placed. It doesn’t run off of the surfaces it is intended to lubricate. Greases can also provide a seal to keep contaminants out of the bearing surfaces. Additionally, semi-solid lubricants tend to form thicker films and are the most effective lubricating ‘dirty’ surfaces.
Both dry and liquid lubricants work in similar fashions. Both reduce friction by preventing surfaces from actually rubbing together. This leaves the question of which is better for use in small arms. As with most things in life, the answer is a bit more complicated than it would first appear.
If you are only considering friction, and are not concerned with other aspects of engineering, then on a smooth clean surface wet lubrication has a clear advantage. However, if we take the nice clean surface and start adding sand and grit, the mechanics get a bit more interesting.
Grit can cause malfunctions in several different ways. The first is that grit simply starts to make contact with moving surfaces and slows them down to the point that the weapon no longer functions. A weapon suffering from this sort of malfunction can usually be cycled by hand, but will not cycle reliably on its own.
The issue is one of equilibrium. Grit is always getting into the weapon and grit is always falling out of the weapon. The question is whether the grit is going in or falling out faster.
This brings us to the popular debate regarding use of wet lubricants in sandy/dusty environments. The primary concern is that the wet lubricant will ‘attract’ dirt. In truth, the wet lubricant doesn’t really attract dirt, rather it ‘holds’ dirt. The difference is subtle but important. A dry lubricant doesn’t prevent dirt from getting into a mechanism; it simply does not ‘hold’ the dirt in place. Not being held in place may mean falling to the ground or it may mean falling into the magazine of the weapon.
Clearly, dry lubricants will allow grit to fall out of the weapon more readily than wet lubricants. This is a clear advantage of dry lubricants. On the other hand dry lubricants are generally not very effective at lubricating (coating) grit that stays in the action of the weapon. Liquid and semi-solid lubricants are better at lubricating and suspending particles of grit, because they tend to form a thicker separation layer.
This means that dry lubricants do tend to keep the weapon cleaner, but wet lubricants tend to allow the weapon run dirtier. Which type of lubricant is better is largely a matter of how clean the weapon is kept and how many rounds you expect to have to put through it -- a weapon gets dirtier as you shoot it.
Those are the pros and the cons. However, at the end of the day you have to pick something to apply to your weapon.
It is the recommendation of White Sound Defense that a reasonably thick (viscosity) liquid or a semi-solid (grease) lubricant be used. These types of lubricants continually redistribute and provide better suspension of gritty particles. Additionally, liquid lubricants lend themselves well to carrying a small easily accessed bottle that can be used for emergency lubrication, especially for crew-served weapons.
At the end of the day there is no magic lube that will allow a weapon to function correctly when filled breach to bore with sand. And no lubricant will change the fundamental nature of the weapon, some designs simply tolerate girt and grime better than others.
Regardless which lubricant you use the most critical aspect of weapon reliability is gun handling. If the weapon is in the field the muzzle should be taped or capped. The dust cover should be closed. Loaded magazines should be periodically unloaded and reloaded to ensure that grit hasn’t worked its way into the magazine. The weapon should be protected and kept clean to the best of your ability.