"Additives are like all the gizmos on your gun - each one does something really cool. But if the wrong guy is in charge, Captain Tacticool becomes Major Tactifool really quick. The wrong additives can screw things up in a hurry."
~Cherry
Educate yourself - Additives
Additives are enhancements to lubricants that give specific performance advantages, similar advances in weapon tech. Earlier tech can 'work just fine', but it has its limitations.
Understanding Additives
Additive packages are all the extra ingredients that provide additional desirable abilities and capacities to your lubricant. In modern machines, they are the hidden ingredients that make or break a lubricant. It's important to emphasize that any professionally designed machine lubricant will have an additive package, because any common machine is going to have operating dynamics that will need both hydrodynamic lubricants and boundary lubricants.
Conceptually, additives are similar to the extra bells and whistles a modern firearm has over a muzzleloader. Most competent hunters are perfectly capable of downing a buck with a .50 caliber Hawken, but that metallic-cartridge Henry re-peater sure is nice for defense. Likewise, the weapon lubrication standards of the early 1800s, bear grease and olive oil, may work on your gun in a pinch, certainly better than nothing, but modern synthetic base-stocks and a carefully chosen mix of additives are to lubricants what high-capacity magazines, optics, and premium bullet designs are to modern weapons.
Just like the overall formulation of a lubricant, additives should be selected for the machinery at hand. For guns, because of their operating environments and the fact that they function almost entirely under sliding dynamics and sheer forces, largely at the boundary level, additives need to cover these bases. Typically, they will be chosen to provide anti-friction, anti-wear, extreme pressure, and anti-corrosion/anti-oxidation properties, which should be mandatory for guns. Viscosity modifiers, while sometimes challenging tribology, are also exceptionally advantageous, as they can keep a lubricant the same consistency in wide temperature extremes. Also helpful can be detergent/dispersant additives, but only in relatively small quantities, as they can quickly negate the ability of boundary lubricants and other boundary additives to do their jobs, by essentially pulling them up from the metal.
The role of anti-friction additives is self-explanatory, simply providing extra lubricity at the boundary level. Molybdenum, Teflon, and graphite are examples of anti-friction additives. Most have a polar charge that attracts them to the base metal of your gun, providing a ‘tribofilm’ of friction-reducing coating, serving as the "black ice" analogy in the Lubricant Regimes segment. Properly selected boundary lubricants also serve as a tremendous fail-safe in the event of a liquid lubricant burning off or drying out - having adhered to the substrate metal, several of these boundary lubricants can withstand temperatures over 2000°F.
Anti-wear additives generally function by laying down a “sacrificial layer” of material over the substrate metal a machine is built from. When contact between moving parts occurs, this material will be worn away first. Some of the most common anti-wear compounds are zinc derivatives, including ZDDP, ZDP, and
A good additive package will enhance each other, but a poor selection of additives can work against each other. Illustrated here is a microscopic ZDDP film smoothing out a friction spot, providing a sacrificial wear layer, while molybdenum coats peaks of exposed substrate metal, with both surfaces separated by a film of oil (blue) - exhibiting proper "mixed regime" lubrication.
others. These molecules are polar, and will lay down zinc 'pads' that, under friction, flash into a phosphate glass 'tribofilm' at the microscopic level, typically on rougher spots or places with greater friction. The unactivated zinc also provides anti-corrosion/anti-oxidation properties, helping mitigate the corrosive effects of many contaminants, such as salt-water or humidity on guns.
A Scanning Electron Microscope image of the slick tribofilm of phosphate glass created by ZDDP, having flashed under friction heat. This can occur while rapidly dry-cycling a gun.
ZDDP was incredibly common in motor oils for decades, and is in fact rather old technology - but it works with excellence. It has seen a dramatic decline in usage in motor oils, however, because it has a tendency to clog catalytic converters. As with many 'green' solutions, the unintended consequences can be damaging. However, ZDDP maintains its place as a valuable anti-wear extreme-pressure additive for other machines, and depending on the variant selected, will activate in a range of friction temperatures, including those found by the manual cycling of a firearm.
Extreme pressure additives provide that extra edge on most machines during ongoing extreme pressures, such as with gear boxes, or ‘shock loading’ – that sudden impact of energy on a relatively small area, that can cause moving metal surfaces to penetrate the fluid-film barrier under extreme force. An EP additive generally functions by laying down a localized film, bonded to the metal sometimes by electrical charge, as with Molybdenum (both anti-friction and extreme pressure in its properties), or by a combination of high pressure and friction heat, as with ZDDP, all to mitigate metal-to-metal contact.
Viscosity modifiers are one of the more interesting additives, especially when applied to a gun lubricant. A key challenge for tribologists is that oils have a strong tendency to thin out as they get hotter. Before multi-viscosity oils were developed, motors often used a thick oil in the summer and a thinner one in the winter. The reason was that a sufficiently thick oil for summer driving - that would thin out to the right weight at high operating temperatures - would be damagingly thick in cold weather. Such oils would not flow well to bearings until heated up, often leaving bearings running in metal-to-metal contact. And thin winter oils would simply be far too thin at the hotter driving temperatures of summer.
To address this, engineers developed polymer viscosity modifiers that react to heat. They are long chain molecules that, when cold, are coiled tightly, but unwind steadily as they warm. In unwinding, they keep an increasingly hot oil the same thickness. The design and amount of a given polymer viscosity modifier in any oil are what allows for the ranges of multi-viscosity engine oils. When applied to the base-stock oil in gun greases, they allow for colder low-end operating temperatures, while assisting in keeping the oil thick enough to stay put as temperatures quickly rise during intense gunfire.