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A 12-gauge shotgun, nominally 18.5 mm (0.73 in), can range from a tight 18 mm (0.71 in) to an extreme overbore of 20 mm (0.79 in). Some also claim an increased velocity with the overbored barrels, up to 15 m/s (49 ft/s), which is due to the larger swept volume of the overbored barrel.
Later in the 1870s, a Swedish captain called D. H. Friberg patented a design which introduced both flapper-locking and the fully automatic recoil operated machine gun. [7] Furthermore, in 1875 a means of cocking a rifle through recoil was patented through the patent agent Frank Wirth by a German called Otto Emmerich. [8]
Comparison of .577 Black Powder Express, .303 British & 8 bore bullets. The most common 8 bore cartridges used paper cases, much like shotgun shells, and true .835 in (21.2 mm) caliber projectiles. A larger version utilising a thin brass case was also available, although it fired .875 in (22.2 mm) projectiles, in reality making it a 7 bore. [5]
For a gun firing under free-recoil conditions, the force on the gun may not only force the gun backwards, but may also cause it to rotate about its center of mass or recoil mount. This is particularly true of older firearms, such as the classic Kentucky rifle , where the butt stock angles down significantly lower than the barrel, providing a ...
The recoil from a fired cartridge (and the action movement) exerts a rearward impulse along the bore axis, which is commonly above the center of mass of the gun. Meanwhile, the gripped areas of the gun, where the user will exert a reactional forward push countering the recoil, is almost always below the gun's center of mass.
Illustration of forces in muzzle rise. Projectile and propellant gases act on barrel along barrel centerline A. Forces are resisted by shooter contact with gun at grips and stock B. Height difference between barrel centerline and average point of contact is height C. Forces A and B operating over moment arm / height C create torque or moment D, which rotates the firearm's muzzle up as ...
The exit end of a choke is smaller by some dimension than the actual bore of the barrel. This difference in diameter is the amount of constriction. For example, for a 12 gauge, the bore diameter of the barrel is nominally 18.5 mm (0.73 in), although different manufacturers do vary their as-manufactured bore from this diameter slightly.
The minimum barrel length for shotguns in most of the U.S. is 18 inches (460 mm), and this barrel length (sometimes 18.5–20 in (470–510 mm) to increase magazine capacity and/or ensure the gun is legal regardless of measuring differences [3]) is the primary choice for riot shotguns. The shorter barrel makes the weapon easier to maneuver ...