Accurizing

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.

[3][4][5][6] 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.

At 100 yd a minute of arc equals 1.047 inches (26.6 mm), and the one MOA group (approximately 1/3 or 0.3 mil) is a traditional benchmark of accuracy.

[14] Over travel is not always considered bad by some, as the force of the trigger finger does not impact on the gun directly after sear release.

Firearms with non-adjustable or coarsely adjustable sights cannot give their holders the ability to reliably shoot on target in changing conditions.

[5] Typical open sights with a blade, post or bead near the muzzle and a notch over the breech are good for quick alignment but far from ideal for accuracy.

Telescopic and reflex sights offer advantages to people with less experience or poor eyesight by bringing both target and aiming point into focus, while "scopes" also magnify and brighten the image.

For shotguns in particular, the placement of the shooter's face on the stock provides the rear aiming point, and the correct drop, toe alignment, and cast-off can greatly enhance accuracy.

High combs and vertical pistol grips are ideal for high mounted target sights or scopes and careful, deliberate shooting such as encountered in traditional target shooting, metallic silhouette, or varmint hunting, as they provide a maximum point blank range and ideal trigger control.

Some target shooting disciplines allow the use of various devices to help support the rifle, and these are often mounted to an accessory rail beneath the forend.

Palm rests are another device that can be attached to the rail, to allow a shooter to lower their off hand and place their elbow into their body for support.

To ensure consistent, repeatable lockup, clearances between moving parts must be kept to the smallest value that will allow proper operation of the mechanism.

[3][4] Clearances cannot be too tight, however, or functionality will be compromised; this is very important in automatic and semi-automatic firearms, where there is a certain amount of energy extracted from the firing of the cartridge that must be used to cycle the action.

[40] In practical terms, this is only a problem for rifles chambered for common military calibers where a variety of different loads exist.

For example, the hammer forging method of manufacture leaves a significant amount of stress in the barrels, which could be addressed through stress-relieving heat treatment.

These changes can affect accuracy either by allowing the action to shift under recoil, or by causing slight but accuracy-destroying bending of the barrel.

This must be wide enough to allow free rotation of the cylinder even when it becomes fouled with powder residue, but not so large that excess gas can be released.

[48] There are two ways to address harmonics; reducing the amplitude with a stiffer barrel, or working with the natural frequency to minimize dispersion.

Either technique greatly increases the stiffness of the barrel by enlarging the average diameter, but this process adds significant weight as well.

Fluting, consisting of grooves machined in the outer surface of the barrel to remove material, can reduce the weight and improve heat dispersion while maintaining most of the stiffness.

One type uses an adjustable damper or pressure bedding point to allow the shooter to find the "sweet spot", where it will do the most good at damping the vibrations that are affecting accuracy.

[52][53] Other tuners work by using an adjustable weight on the muzzle to alter the length of the resonant portion of the barrel, and allowing the frequency to be matched to the ammunition.

In a firearm the projectile propulsion is provided by an exothermic chemical reaction, and in an airgun is it provided primarily by mechanically compressed gas, typically either air or carbon dioxide (CO2), though these gases are used primarily for convenience and some airgun variants run on other gases, such as refrigerants like R-134a commonly used in airsoft guns, or hydrogen used in light-gas guns.

[56] The most powerful systems will produce velocities near or exceeding the speed of sound with lightweight pellets; this, however, is not a good thing where accuracy is concerned.

The commonly used airgun diabolo pellets have a poor ballistic coefficient, and quickly lose velocity; when they drop below the speed of sound, they will often tumble.

The (at the time) US$40 Daisy, with a better rear sight and an adjustable trigger added, shot as well as the US$400 Olympic class air pistols it was competing against.

The ability to vary the power, however, is the pump airgun's major disadvantage when it comes to accuracy, as it makes it very difficult to get a consistent charge.

The preferred method is a very loose hold, to allow the gun to move back; this means that a piston airgun will not shoot the same from a bench.

[62] Spring driven pistons also respond well to accurizing; careful fitting of parts and use of quality lubricants and spring damping tar can reduce the level of vibrations and improve accuracy[63] CO2 is commonly found in multishot airguns, from the cheapest plinkers to Olympic class target guns, though the latter are facing competition from regulated precharged pneumatics.

The downside to these is that the small quantity of CO2 liquid cools down quickly, leading to a rapid drop in velocity and a changing point of impact.