Firearm maintenance (or gun care for short) is a series of periodic preventive maintenance procedures aiming to ensure the proper function of a firearm, often with the use of a variety of specialized tools and chemical solutions. Typically such maintenance is performed by the owner of the firearm using either simple methods such as cleaning the firearm with oil or other cleaning solutions, or more sophisticated practices such as lubricating moving parts with oil/grease and re-coating exposed surfaces with protective finishes such as varnishing or bluing.
When a firearm presents with physical damage related to the ordinary use of the firearm, or when a firearm malfunctions in a life-threatening manner, a professional gunsmith should perform advanced maintenance to determine if the firearm is repairable and/or safe to shoot anymore.
An inadequately maintained firearm will often accumulate excessive fouling and dirt within the barrel and receiver, which not only can clog up the rifling and decrease the firearm's accuracy and precision, but can also interfere with the proper operation of the action and lead to potentially dangerous malfunctions. Furthermore, some of the fouling and dirt found is either corrosive themselves, or capable of making the firearm vulnerable to rusting and wear, and this can lead to irreversible damages to the firearm over time.
The consequences of neglecting proper maintenance can be serious. For instance, during the Vietnam War, the newly issued M16A1 assault rifle was distributed to US troops with marketing literature from Colt Firearms claiming that the weapon was self-cleaning, which implied to many to mean that it did not have to be routinely maintained. However, this attitude compounded the rifle's design flaws and made the weapon notorious for repeated failures in combat, which led to needless casualties among US forces. Once the problem was acknowledged by the US military, the weapon was not only subject to upgrades, but US troops were also trained in proper maintenance of the weapon and supplied with cleaning kits and an illustrated pamphlet on the subject by Will Eisner.
The ordinary firing action releases fine particles of gunpowder, metals (mostly lead and copper from the bullet moving over the rifling) and other contaminates into the inner spaces of a firearm, which may cause malfunctions or in rarer cases of extreme buildup may raise the barrel pressure too high causing the firearm to explode (catastrophic failure) upon being fired. It has been widely reported that firearms without a spring to control the inertia of the firing pin require constant cleaning of the bolt assembly, as extremely dangerous phenomena such as slamfire may occur. Slamfire is a malfunction in which a firearm which is normally semi-automatic may temporarily and involuntarily become fully automatic, firing repeatedly — without another pull of the trigger — until the firearm is out of ammunition.
Every major firearms manufacturer provides detailed information on the proper methods used to disassemble, clean and then reassemble a firearm they produced. This information is usually packaged with the firearm. In the event that this information is not present with the firearm at the point of purchase, it is advisable to ask the manufacturer where this information may be obtained. For safety reasons the manufacturer's directions for cleaning, maintenance and care should always be followed.
Firearms produce massive momentary forces upon firing a bullet. A typical 9mm projectile produces a maximum of 34,084 psi (2,350.0 bar) of pressure in the instant of firing. The amount of pressure a firearm may endure for the first few milliseconds after the cartridge fires can be over 2,300 times more than the normal atmospheric pressure. Therefore it is important for the safety of the shooter, and the longevity of a firearm that it is properly lubricated as per the manufacturer's specifications.
When in an extreme and life-threatening situation such as preparing for combat, the manufacturer's recommended lubricants may not be available to soldiers, or others who may enter these scenarios. If there is time to perform firearm maintenance before a life-threatening emergency (such as daily cleaning of a rifle in a combat zone) it may become necessary to use other sources of lubrication, as a firearm will function better with some lubricant than it will with none. One United States Marine Corps sergeant recounts that synthetic motor oil performed better than standard military issued lubricant in extreme conditions. However it is advisable to immediately return to the standard recommendation of the firearm manufacturer when conditions allow.
It is critically important that a firearm is free of ammunition before beginning maintenance. The National Rifle Association teaches gun owners that "before cleaning your gun, make absolutely sure that it is unloaded. The gun's action should be open during the cleaning process. Also, be sure that no ammunition is present in the cleaning area".