US 3496667 A
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Feb; 24, 1970 E. u. LOWRY 3,496567( CHOKED SHOTGUN WITH RIFLED BARREL Filed Jan. 4, 1968 2 Sheets-Sheet E DWARD D. LOWRY INVENTORI ATTORNEY Feb.
Filed Jan. 4, 1968 2 Sheets-Sheet 2 STANDARD SKEET BARREL 1.2
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RAO/AL DSTANCE FROM CENTER OF PATTERN- (IN) i INVENTORZ EDWARD &Low/?y 7% exw/7%@ ATTORNEY 3,496,667 CHOKED SHOTGUN WITH RIFLED BARREL Edward D. Lowry, New Haven, Conn., assignor to Ohn Matheson Chemical Corporation, a Corporation of Virginia Filed Jan. 4, 1968, Ser. No. 695,696 Int. Cl. F41c 21/00 U.S. Cl. 42-78 Claims ABSTRACT OF THE DISCLOSURE An improved barrel for a shotgun having a full choke at its muzzle end and rifiing having a rate of twist deter mined by the formula T=1rBR/P wherein T is equal to the rate of twist in inches per revolution, B is equal to the bore diameter of the barrel in inches, R is equal to the desired range in inches, and P is equal to the radius of the desired pattern in inches.
This invention relates generally to firearms. More par ticularly, it relates to a `barrel for a shotgun intended for firing shot or pellets.
A barrel constructed in accordance with this invention is particularly adapted for a shotgun for use in skeet Shooting. A typical skeet field has two houses which contain traps for throwing the clay pigeons or targets. One house is called the high house and the other the low house, since one starts its targets high and the other low. The targets from each house always follow the same path. The angle of fiight from each house is not directly opposed, but is pointed slightly away from the Shooting posts. The two flight lanes tend to cross in the center of the field some ten feet beyond the line drawn between the houses. There are eight Shooting positions, seven of them being spaced about a semicircle with the first position at the high house and the Seventh position at the low house and Stations two through six evenly spaced along the semicircle between them. The eighth station is positioned at the center of a line running between the high and the low house. It will thus be seen that all the Shooting positions, except number eight, are equdstant between a point where the two target flight lanes cross. Most skeet Shooters try to break the target Somewhere near this crossing point. In view of this fact, and in View of the fact that the shots at the number eight station are very close, it has been determined that a range of 20 yards is the best figure for use in determining the particular pattern of the shot. The ideal shotshell attern for use with skeet has been found to be that wherein all the pellets in the load would fall within and be evenly dis tributed across a 30 inch circle at 20 yards.
With conventional ammunition and a typical skeet gun it has 'been found that although 75 to 80 percent of the shot will fall within the 30 inch circle at 20 yards, the distribution of the pattern is such that the density of the pellets is very high near the center of the circle and relatively low at the outer portions of the circle.
Although the degree of choke of a shotgun can influence the dispersion of the shot, it does not appear able to overcome the problem of uneven distribution. For eX- ample, the barrel of a typical skeet gun is usually provided with a cylnder bore or modified choke. A trap gun is usually provided with a full choke. In the case of the skeet gun, 75 to 80 percent of the pellets can be placed in a 30 inch circle at 20 yards. The dispersion of the pellets to provide this pattern is caused principally by deflections to the pellets which occur'in the muzzle. As the column of shot emerges from the muzzle, it is caught between two forces. Once force is the acceleratng force of the wad acting in the direction away from the muzzle 3,496,667 Patented Feb. 24, 1970 of the gun and the other force is the decelerating force due to air resistance actng on the shot in the direction toward the muzzle of the gun. These two forces acts to compress the shot column and result in lateral movement of the pellets as they emerge from the muzzle. In the case of the full choke barrel, the wad is decelerated due -to the construction in the barrel and the pellets are in a sense squirted out of the muzzle. Accordingly, the shot col umn is not subjected to the "anvil elfect prevalent in a cylinder bored shotgun with the result that the pellets start their journey with all of them traveling toward the center of the eventual pattern. They will, however, be individually deflected due to the fact that their surfaces are slightly uneven and thus the aerodynamic pressure on each pellet will be unbalanced enough to cause a mildly erratic flight. Accordingly, in the case of a full choked firearm the pellets will not have strayed very far by the time the load reaches 20 yards and to percent of the pellets Will pass through a 10 inch circle at this range. Accordingly, to obtain a attern that is wide enough at 20 yards, a bore is required that will permit the pellets to have a relatively large degree of lateral movement as they emerge from the muzzle.
Accordingly, in view of the discussion above on the causes of dispersion, most skeet guns have little, if any, choke. However, as has been stated before, even though the dispersion is deemed satisfactory, the density obtaned with the typical skeet gun is not satisfactory since a high proportion of the pellets are concentrated near the center of the pattern and relatively few near the edges of the pattern.
Accordingly, it is an object of this invention to provide a barrel for a shotgun which will provide the proper dispersion with even distribution across a given pattern.
More particularly, it is an object of the present invention to provide a barrel for a shotgun which is capable of placing over percent of the pellets from a gven load in a 30 inch circle at 20 yards with relatively even distribution across the circle if desired.
Still another object of the present invention is to provide a barrel for a shotgun to be used in connection with the game of skeet which will enhance the chances of breaking a target in the event of an error in ain.
These and other objects of the invention may be accomplished through the provision of a shotgun barrel having a full choke and being rifled from its muzzle to the shell receiving cham'ber with a twist deemed by the formula T=7rBR/P wherein T is equal to the rate of twist in inches per revolution, B is equal to the bore diameter of the barrel in inches, R is equal to the desired range in inches, and P is equal to the radius of the desired pattern in inches.
The advantages of the present invention will become more apparent upon the reading of the following description and by reference to the accompanying drawings in which:
FIGURE 1 s a transverse cross sectional View of a portion of a gun barrel embodying the invention;
FIGURE 2 s a transverse cross sectional view taken on the lines 2-2 of FIGURE 1;
FIGURE 3 is a diagrammatic View showing the relationship of the range and desired pattern used in ascertaining the rate of twist of the rifling of the barrel; and
FIGURE 4 is a graph comparing the pellet density obtainable with a standard skeet barrel with that of a barrel constructed in accordance with the present invention.
Referring to the drawings and particularly to FIG- URE 1, the forward portion of a shotgun barrel 2 is shown. The muzzle end of the bore of the barrel 2 is constricted to form what is known in the art `as a full choke as indicated at 4. Although the amount of constriction will vary in accordance with the particular gauge of shotgun Table I provides an indication of the internal diameter A of the internal bore through the choke port on 4 and the internal diameter B of the bore of the barrel for the various common gauge shotgun barrels.
The entire effective length of the barrel 2 is rifled including the choke portion 4 thereof. By effective length is meant the length from the muzzle end to the forward end of the tapered shotshell receiving chamber. If desired, the chamber could also be rifled, but obviously, it would not have any effect on the shot charge because of the shell. The twist rate of the rifiing is constant throughout its length. In the preferred embodiment of the invention as shown in FIGURE 2, there are eight rifiing grooves 6 evenly spaced about the internal surface of the bore of the barrel 2. The depth of the grooves 6 may vary somewhat keeping in mind the fact that if the grooves are too deep, the barrel may be weakened because of its relatively thin wall thickness. It has been found that a depth of .05 inch is satisfactory.
The rate of twist is determined by taking into consideration the bore B of the barrel, the desired range, and the desired width of pattern. As shown in FIGURE 3, points X and Y indicate diametrically opposed points on the circumference of the pattern. The radius of the pattern is indicated by P. Theoretically, it is desired that .the outermost pellets would take the path indicated by lines 8 and 10 and hit the pattern at points X and Y. However, the theoretical is not attainable due to aerodynamic pressure so that between 80 and 90 percent of the pellets are within the pattern area. R indicates the range which is the distance from the end of the bore of the barrel to the center of the pattern.
In accordance with this invention it has been determined that the rate of twist for a full choked shotgun barrel can be determined by the formula T=7rBR/P, where T is equal to the twist rate in inches per revolution, B is equal to the bore diameter in inches, R is equal to the range in inches, and P is equal to the radius of the desired pattern circle in inches, and 'r is equal to the standard dimension of approximately 3.1416.
As has been discussed above, for skeet Shooting, it is desired that a high proportion of the pellets should be contained within a pattern having a 30 inch diameter at a range of 20 yards. Accordingly, when rifiing a barrel in accordance with the preferred embodiment of this invention the twist rate will be determined by the above formula with B being the bore diameter of the particular gauge gun, the range being 20 yards or 720 inches, and P, the radius of the pattern circle, being between 12 and 15 inches. In the case of the exceptional shooter it may be desirable to reduce P to a value below 12 inches down to about 10 inches.
Table II, set forth below, gives the range of desirable twist rates for various gauges as calculated by using the above formula with the bore diameter as set forth in Table I, a range of 720 inches, and a pattern radius of from 12 to 15 inches TABLE II Twist Rate Gauge: (inches/re 12 110 to 138 28 83 to 104 .410 61.8 to 77.2
It is to be understood that in the case of the exceptional shooter, the value of P can be as low as 10 inches. In this case, the upper value of the Twist Rate shown in Table II would be increased.
As shown by Table III, it will be seen that the twist rate of the rifiin of the present invention is substantially higher than that used in rifies of the type firing a bullet.
TABLE III Twist Rate Caliber: (inches/rey.) .22 short 24 .22 long rifle 16 .220 swift 14 .30/30 12 .30/06 10 .32 special 16 .375 magnum 12 Accordingly, it must be appreciated that the rifiing used in the present invention is not of the same twist rate as normally used, and thus cannot be considered the normal degree of rifiing as commonly contemplated in the art.
FIGURE 4 graphically depicts the pattern results of a standard sheet barrel and the improved rifled full choked shotgun constructed in accordance with the present invention. For the purpose of comparison the shotgun constructed in accordance with this invention had a 12 gauge full choked barrel and a twist rate of 129 inches per revolution.
As can be seen from FIGURE 4, with the standard skeet barrel the pellet density is highest in a range from about 0 to 2 inches from the center of the pattern and steadily decreases as you move farther away from the center. The improved shotgun having a barrel constructed in accordance *with the present invention has a lower pellet density in the range from 0` to 2 inches, but the density remains fairly even as you move away from the center of the pattern up to about 10 inches where it begins tapering off. However, in the range of from 8 to 14 inches from the center of the pattern, the pellet density is greater than that of the standard skeet barrel. The standard skeet barrel will place about 75 percent of the total shot in a 30` inch circle at 20 yards. With the full choked barrel of 129 in./rev., about 86.4 percent of the pellets are placed in a 30 inch circle at the same range. Accordingly, with the present invention not only is the distribution of the pattern better than that of a standard skeet barrel with a higher proportion of the pellets landing in the desired pattern radius, but also, the distribution of the pellets within the pattern is better due to the fact that the density throughout the entire pattern is more constant and more pellets are positioned near the periphery of the pattern.
As a further example of the eectiveness of this invention, a plurality of 12 gauge full choked shotguns were fired with their barrels rifled at a twist rate of 143 inches per revolution. With these firearms, about 89.5 percent of the total shot was placed in a 30` inch pattern at 20 yards. As shown in FIGURE 4, the distribution of the pellets is similar to that of the barrel having a twist rate of 129 inches per revolution, except that the density was higher. Thus rifiing in a 12 gauge shotgun of about 145 inches per revolution would be advantageous under certain circumstances.
The combination of the rifiing and the full choke results in the improved pattern characteristics. Due to the rifiing, the shot charge is rotated about its axis giving each pellet a peripheral velocity. This velocity is directly proportional to the distance of the pellet to the axis of the bore of the barrel. Thus, the outstide pellet will be traveling twice as fast as the pellets intermediate the outside layer and the center. As the column of shot leaves the muzzle, each pellet will keep its peripheral velosity which is now a velocity directed in a straight line going away from the pattern center. '1'hus, by giving the barrel the proper riing, so that the outside pellet travels inches outwardly by the time the whole load has traveled yards, the pellets should all be evenly distributed across a inch circle. However, in order to make this work it is necessary to eliminate all sources of dispersion of the pellets. Accordingly, the barrels must be full choked so as to elminate the anvil efiect described above. However, due to the uneveness of the pellet surfaces, the aerodynamic pressure on each pellet will be unbalanced causing a slightly erratic fiight with the result that the theoretically possible perfect pattern of percent and even distribution cannot be obtained. However, as indicated above, it is possible to obtain 89.5 percent of the pellets in a 30 inch circle at 20 yards with a distribution that is more even than that obtainable with the standard skeet barrel.
What is claimed is:
1. In a shotgun, a barrel having a shotshell receiving chamber adjacent one end and a full choke at its muzzle end, the bore diameter of said barrel being about .730 inch, said choke having an internal diameter of between about .694 to .699 inch, said barrel being rified at least from the muzzle end of the choke to the forward end of the shotshell receiving chamber, said rifiing having a rate of twist of from to inches per revolution.
2. In a 16 gauge shotgun, a barrel having a shotshell receiving chamber at one end and a full choke at its other end, said choke having an internal diameter of between about .640 to .645 inch, said barrel being rified at least from the muzzle end of said choke to the forward end of said shotshell receivng chamber, said rifling having a rate of twist of from about 101 to about 121 inches per revolution,
3. In a 20 gauge shotgun, a barrel having a shotshell receiving chamber at one end and a full choke at its other end, said choke having and internal diameter of between about .590 to .595 nch, said barrel being rified at least from the muzzle end of said choke to the forward end of said shotshell receiving chamber, said rifling having a rate of twist of from about 92.7 to about 116 inches per revolution.
4. In a 28 gauge shotgun, a barrel having a shotshell receiving chamber at one end and a full choke at its other end, said choke having an internal diameter of between about .528 to .532 inch, said barrel being rifled at least from the muzzle end of said choke to the forward end of said shot shell receiving chamber, said rifiing having a rate of twist of from about 83 to about 104 inches per revolution.
5. In a .410 gauge shotgun, a barrel having a shotshell receiving chamber at one end and a full choke at its other end, said choke having an internal diameter of between about .390 to .393 inch, said barrel being rified at least from the muzzle end of said choke to the forward end of said shotshell receiving chamber, said rifiing having a rate of twist of from about 61.8 to about 77.2 inches per revolution.
References Cited UNITED STATES PATENTS 592,437 10/ 1897 Oberhammer 42-78 BENJAMIN A. BORCHELT, Primary Examiner CHARLES T. JORDAN, Assistant Examiner U.S. Cl. X.R. 42-79