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For naval rifles, the initial change was to actual bore, thus facilitating the manufacture of standard projectiles. They then began to measure the effective length (and therefore range) of the weapon in calibers. These are a measure of the standardized length of the barrel versus the rifled bore of the barrel.
While modern firearms are generally referred to by the name of the cartridge the gun is chambered for, they are still categorized together based on bore diameter. [citation needed] For example, a firearm might be described as a "30 caliber rifle", which could accommodate any of a wide range of cartridges using a roughly 0.30 inches (7.6 mm) projectile; or as a "22 rimfire", referring to any ...
Comparison of milliradian (mil) and minute of arc (moa).. Since adjusting the point of impact to match the point of aim is relatively simple with any type of adjustable sights, the primary goal of accurizing is to increase the precision of the firearm, which is generally measured by looking at the dispersion of a number of shots fired at the same point of aim.
The barrel and overall length were shorter than a traditional rifle and it had a pistol grip to hold the weapon more securely in automatic fire. The principle of this weapon — the reduction of muzzle impulse to get usable automatic fire within the actual ranges of combat — was probably the most important advance in small arms since the ...
Since barrel length is limited by practical concerns to about arm's length for a rifle and much shorter for a handgun, increasing bore diameter is the normal way to increase the efficiency of a cartridge. The limit to bore diameter is generally the sectional density of the projectile (see external ballistics).
Chamber illustration indicating the various sections of a typical rifle chamber. The freebore is the cyan colored section just ahead of the neck. In firearms, freebore (also free-bore, free bore, or throat) is the portion of the gun barrel between the chamber and the rifled section of the barrel bore. The freebore is located just forward of the ...
For example on an AR-type rifle, the mil-spec distance from center of bore to top of rail is 1.211 inches, or approximately 31 mm (1.2 in). The mount height itself, that is the distance from the top of rail to center of scope, varies, but typically lies around 36–38 mm (1.4–1.5 in) (higher and lower mounts are also readily available).
Because the U.S. 1934 NFA regulations set the minimum rifle barrel length at 16 inches (410 mm), Charter Arms made the barrels of the Explorer I rifle and Explorer II pistol non-interchangeable to prevent installing the pistol barrel on the rifle. The AR-7 barrel has an alignment lug that mates a notch in the receiver.