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If your serious about accurate shooting - you either have or should read this:
Crandall; David L. (Idaho Falls, ID)
Exsplains: Ballistic Optimizing System (U.S. Pat. No. 5,279,200)
Accuracy as it relates to guns, is defined as the ability of the gun to cause a projectile to arrive at or near to an intended location some distance from the gun. A gun which can deliver its projectiles consistently closer to that location is said to be more accurate. Accuracy is clearly a desirable attribute of a gun since the energy of the projectile can only be put to use effectively if the projectile can be brought to the intended target.
Inaccuracy results primarily from angular deflection of the paths of a plurality of projectiles from the average path of the projectiles as a group, given that the aiming point is the same. In earlier times, much of this angular deflection was caused by deflection of the projectile itself after it left the gun muzzle. Poor projectile shape, plus mass and shape eccentricity caused by fabrication technique or deformation during firing, were accuracy reducing influences. Addition of rifling in gun bores to impart stabilizing spin to the projectiles allowed the use of improved shapes. Self-contained cartridges combined with successful breech loading systems were developed. Stronger projectiles with jackets of copper or other materials resulted in greater resistance to deformation during firing. Other improvements included smoother gun bore surfaces of very uniform dimensions closely matching the diameter of the projectiles and better gun chamber dimensional control resulting in close alignment of the projectile with the bore. Concentricity and uniformity in cartridges has also been greatly improved over time.
All of the above advances have reduced the angular deflection of projectiles after they depart the muzzle leaving variations in angular deflection of the muzzle itself during firing as a significant negative influence on the accuracy of guns. Angular deflection results from the forces generated during firing. A number of factors acting in conjunction with the forces generated during firing produce effects acting perpendicular to the gun bore. Some factors include uneven bearing of the cartridge case on the bolt face due to cartridge or bolt irregularities, uneven bearing of bolt locking lugs on receiver mating surfaces, asymmetric flexing of the receiver under the loads of firing due to asymmetry of the receiver, and inconsistent interferences between the gun and supporting structures to include the shooter, in the case of small arms, or the gun carriage in the case of artillery. However, the most common single factor producing force components acting perpendicular to the gun bore results from the fact that the mass center or center of gravity of the gun, including all attachments, is not normally located concentric with the axis of the gun bore. The forces produced by the pressure of the propellent gases act rearward along the axis of the gun bore. These forces are resisted by the mass of the gun but because the mass center is offset from the bore, a couple results, thereby producing accelerations of the gun barrel in directions perpendicular to the axis of the bore. These perpendicular accelerations, acting along the unsupported sections of the gun barrel are resisted by the mass of the gun barrel causing temporary elastic bending of the gun barrel, and angular deflection of the final segment of gun barrel adjacent to its distal end. This final segment of barrel is called the muzzle. The development of these forces which produce gun muzzle angular deflection increase and diminish in very short periods of time, on the order of one millisecond for modern high powered rifles, as the pressure inside the gun cartridge increases to a peak and then declines as the projectile moves further down the gun barrel to be finally released as the projectile leaves the muzzle. The bending of the gun barrel is, therefore, also a transient event resulting in changes in the amount of bending over the very short time period while the projectile is in the barrel. Small variables, which may include such things as changes in the pressure profile and/or drag of the projectile inside the barrel from shot to shot, tend to change the timing of projectile departure relative to the angular position of the muzzle. This in turn results in dispersion of projectile impacts at the target.
The prior art applies two primary techniques to mitigate the negative effects of angular deflection in the muzzles of guns during firing. The first technique consists of increasing the section modulus of gun barrels thereby reducing the magnitude of deflection under perpendicular accelerations. This is usually achieved by simply increasing the outside diameter of the gun barrel, although fluted or sleeved barrels are sometimes used. The second technique consists of adding a small fixed or adjustable weight to the end of the gun barrel placed in such a position to cause a period of reduced rate of angular deflection at the muzzle to coincide with the average time of projectile exit. Both of these techniques have drawbacks and limitations. Fluted and sleeved barrels are usually heavier than their conventional counterparts of the same length. Larger diameter barrels are always heavier. Barrel weights can only be correctly positioned or "tuned" empirically and also typically perform best with only one cartridge loading condition. Retuning is required for any change in cartridge or cartridge components including changes in brand, bullet type, weight, or powder charge. Further, both of these techniques can only reduce, but not eliminate, angular deflection of gun muzzles. Since some variation in the timing of projectile release will always remain, these techniques cannot filly optimize the accuracy of guns.
State of the Art in Recoil and Muzzle Rise Reduction:
Gas pressure released by the ignition of the powder in a gun cartridge acts on the base of the projectile to propel it along the bore of the gun. This same gas pressure acts on the breech mechanism of the gun to produce a recoil force and motion. As has been previously explained, this force acts along the axis of the gun bore to produce not only rearward acceleration of the gun, but also perpendicular accelerations on the gun barrel. Since the mass center of the typical gun is below the axis of the bore, the acceleration of the gun barrel is generally upward. Propellent gases also act to increase recoil if their mass is allowed to exit the gun barrel along the axis of the bore. Both muzzle brakes and compensators serve to redirect the propellent gases from their path along the axis of the gun barrel and, therefore, reduce recoil. A number of devices have been developed as attachments to the muzzles of guns to reduce recoil and muzzle rise. Today, devices which redirect propellent gases to reduce the recoil of guns are called muzzle brakes, although any device which reduces recoil force may also reduce muzzle rise. Those devices which intentionally direct more of the gases upward to reduce muzzle rise are usually called compensators. A great many variations of muzzle brakes and compensators exist, however, they have some common characteristics. They are all attached to or are made integral with the gun barrel distal end. They include one or more chambers with a diameter significantly larger than the projectile. Most all include one or more baffles of a diameter smaller than the chamber or chambers but still larger than the projectile, which serve to isolate the chambers and baffle the flow of propellent gases from continued motion in the direction of the projectile. Compensators are characterized by a hole or holes which penetrate into the chamber or chambers and which serve to direct propellent gases upward or upward and backward. The jetting effect of these gases serve to create a downward or downward and forward force which lessens both muzzle rise and recoil. In the case of muzzle brakes, the holes are arranged in opposing pairs or around the full perimeter of the chambers. Muzzle brakes release the propellent gases, thereby lessening the recoil, but do not generally use the jetting force deliberately to reduce muzzle rise. Muzzle brakes and compensators are not normally considered accurizing devices because they act only after the projectile has left the barrel. They do, however, constitute a small added mass which, when properly positioned on the barrel, can serve to improve accuracy as has previously been described. This is the case with the Ballistic Optimizing System (U.S. Pat. No. 5,279,200) which incorporates a muzzle brake with position adjustment features so it can be used also as an accuracy tuning mass.
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