Accurizing is the process of improving the accuracy and precision of a gun (firearm or airgun).For firearms, accuracy is the ability to hit exactly what one is aiming at, and precision is the ability to hit the same place over and over again in a repeatable fashion. Both are the goals of accurizing, which generally concentrates on four different areas:
Usability: Enhancements that give the shooter a firmer and more controlled hold on the firearm, as well as a more consistent trigger pull. Better design ergonomics is often employed, such as adjustable buttstocks and grips with more vertical angles that are natural to the human hand and wrist (e.g. pistol grip). Spirit levels are often mounted to prevent canting, which can vary the points of impact. Weapon mounts such as bipods, monopods, benchrests, shooting sticks or simply sandbags can provide a more stable and relaxed platform for the shooter, and devices such as muzzle brakes or compensators can also be used to help counter the muzzle rise from recoil and re-establish aim faster and more precisely for repeated firing. The use of suitable slings can also help shooters to stabilize their aim when shooting off-hand while standing or squatting.
Tolerances: Parts that better fit together will shift less, or shift more consistently, under recoil. Rifle bedding is one of the most common practices of such accurizing procedure. Adequate screw torque setting between the action and the stock is also important for the overall rigidity of the system. Some companies, such as Savage Arms, have even introduced features like floating bolt head to provide better bolt-breech engagement for more adequate breech seal and headspacing.
Harmonics: The act of firing a gun generates a rapid pressure increase within the barrel bore, causing the barrel to resonate and vibrate in a rope-like fashion. The resultant harmonic oscillations of the barrel affect the terminal phase of the projectile's internal ballistics and in turn the initial status of its external ballistics, and therefore need to be minimized or tuned to limit their effects on accuracy. Generally the harmonic effects are proportional to the square of the barrel length, and so are generally only of concern in long guns such as rifles but not handguns. Some external accessories, called tuners or de-resonators, can also be mounted onto the barrel to alter the harmonic wave pattern so that the node is shifted as near to the muzzle as possible. Airguns have significantly lower barrel pressure, and therefore are far less affected by barrel harmonics than firearms.
Projectile propulsion consistency: In airguns, the inbuilt powerplants themselves provide the propulsive force to the projectile, so tuning the gun alone is usually sufficient for accurizing as long as the projectiles' weights and shapes are uniform. Firearms, however, rely purely on oxidative chemical reaction of the powder within a cartridge to provide propulsive force, and any slight variations in powder load and combustion efficiency will affect the internal ballistics of the gun, even if the projectile weights and shape are the same. This means that in addition to the gun itself, consistent ammunition performance is also extremely critical for accuracy with firearms. While some manufacturers produce match-grade ammunition with smaller tolerances, it is common for shooters of high-precision disciplines to handload and fine-tune their own ammunition. Furthermore, the rapid gas expansion that occurs when the projectile leaves the muzzle also barometrically affects flight behaviour, so muzzle devices such as flash hider and suppressor can also be used to modulate the escaping gas and improve the consistency of shots.The key to an accurate firearm is consistency. Getting everything to happen the same way for every shot is key to producing small groupings, and there are a large number of issues to be addressed in achieving an accurate firearm. The keys to firing an accurate shot are a firm but not overtight grip, the ability to get a good sight picture and a controlled squeeze of the trigger. The ability to manage recoil is also important in heavily recoiling calibers, both to aid in possible additional shots, and to prevent the user from developing a fear of the recoil.