Patent Publication Number: US-2011048269-A1

Title: Rifle Cartridge

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention lies in the field of interior ballistics and relates, more specifically, to a novel cartridge. Ballistics is generally divided into three distinct categories, namely, interior ballistics, exterior ballistics, and terminal ballistics. Here we deal exclusively with interior ballistics. 
     A variety of parameters influence the ballistic behavior of powder-accelerated ammunition. In terms of the interior ballistics, the shape of the and dimensions of the cartridge shell (relative to the interior bore dimensions of the gun chamber), the amount and characteristics of the propellant (powder) charge, the primer and the primer vent connection to the main cartridge chamber are some of the primary aspects of interior ballistics behavior. Pressure and head space parameters are also important and they must be balanced against the other parameters. 
     This invention relates to rimmed cartridges and to rimless cartridges. Rimmed cartridges are provided with a base that has a wider diameter than the main body of the cartridge. The wider base forms a rim around the cartridge bottom with which the cartridge rests against the entry rim of the chamber. The base of rimless cartridges typically has the same or even smaller diameter than the body. The cartridge sits in and braces against the chamber walls to define its insertion depth. An extraction groove remains outside the chamber so as to allow the cartridge shell to be removed after the bullet has been fired. 
     In the following description the novel cartridge (the “0.270 Schuster”) will be compared primarily with the 0.308 Winchester (i.e., the 7.62×51 mm NATO centerfire cartridge) and with the 0.270 Winchester. The former is probably one of the most popular and successful hunting, competition, and sharp-shooting cartridges. 
     The 0.308 Winchester was adopted with a standard 146 grain bullet. Loading manuals present data for bullet weights up to 200 grains. Bullets weights of 168 provide for very impressive performance in serious target competition. Further, generally heavy weighted bullets are a good choice for shooting longer distances. Bullet weights from 174 to 190 grains are especially popular for long range shooting. 
     These bullet weights, however, result in considerable recoil, which is unacceptable to many shooters. Mid-range weights from about 145 to 155 grain deliver acceptable recoil performance for most shooters. The 0.308 Winchester cartridge is overpowered for many shooting applications and the recoil presents a problem with regard to gun control in time-limited shooting disciplines. 
     BRIEF SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a rifle cartridge, which overcomes the above-mentioned disadvantages of the heretofore-known devices of this general type and which provides for a new cartridge with a lower energy potential but with similar or even better features and ballistics for the preferred bullet weights at approximately 145 to 155 grain. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a rifle cartridge, comprising:
         a shell case having a case length between 1.900 inches and 1.950 inches and having a neck forming a mouth for a standard .270 caliber bullet;   a shoulder adjoining said neck and widening from said neck to a diameter of between 0.445 inches to 0.465 inches;   a shell body adjoining said shoulder and having an interior forming a main powder chamber for receiving an explosive charge;   a head adjoining said shell body and forming a base of said shell case, said head having a primer pocket formed therein communicating with said main powder chamber through a vent hole formed between said primer pocket and said main powder chamber.       

     In accordance with an added feature of the invention, the shoulder is formed by a conical wall enclosing an angle of 20 to 45 degrees relative to a longitudinal axis of the cartridge. This range of angles is particularly suited for rimmed cartridges. In the context of a rimless cartridge, the range is limited to 25 to 45 degrees. 
     In accordance with a preferred embodiment of the invention, the angle is 30°, i.e., the shoulder walls enclose an angle of substantially 60° with one another. In the most preferred embodiment, the angle is 60° 00′28″. 
     In accordance with an added feature of the invention, the shoulder walls merge towards an imaginary apex lying on the longitudinal axis of the cartridge and the imaginary apex lies within the neck. 
     In accordance with a preferred embodiment of the invention, shell case has a case length of 1.924 inches and the shoulder widens to a widest diameter of 0.450 inches. 
     In accordance with a concomitant feature of the invention, the neck has a diameter of substantially 0.315 inches to avoid confusion with 6.5 mm caliber cartridges. 
     The invention described herein presents a new cartridge which is at a lower energy potential but has similar or better features and ballistics for the preferred bullet weights at approximately 145 to 155 grain, as compared with the prior art. 
     The novel cartridge uses a reduced case capacity compared with the 0.308 Winchester cartridge. The heat from the burned powder charge is lower. This will result in a lower system and barrel warming result in a longer action and barrel life. 
     Bullets with good aerodynamic features are defined by a long ovigne Spitzer bullet design in combination with a boat tail bullet form. This will reduce air resistance and result in higher energy and bullet speeds and less bullet drop over longer shooting distances. 
     Bullet weights for shooting at longer distances or accuracy shooting are mostly above average bullet weights. Most in the upper half or third of the usable bullet weights are recommended for the caliber. 
     The cartridge chamber of the rifle must, of course, be formed to correspond with the cartridge dimensions and the bullets. Most similar cartridges have a short bullet overlap and transition to the grooved barrel. 
     The shoulder angle to the mid axis influences barrel life and shooting precision. A flat angle promotes burning powder fragments pushed into the barrel from burning powder charge. A higher angle of approximately 30 degrees to the mid-axis (double 60 degrees from shoulder to shoulder) supports burning of most powder fragments in the cartridge chamber. Much higher angles can cause misfire in repeating or self-loading rifles. 
     The novel cartridge is a good balanced cartridge with moderate recoil, controllable for rapid firing reduced action and barrel heating and stress. The novel cartridge has a relatively long bullet overlap which is comparable with the popular good balanced 6.5 mm target bullets. This overlap allows the use of a new good balanced aerodynamic styled target bullet which previously did not exist at this bullet weight and caliber. 
     Although the cartridge starts at a reduced power level relative to the 0.308 Winchester, it results in better data of speed energy and bullet drop at the same mid-weighted bullet range. See Tables 1 to 3. 
     The preferred range of bullet weights from approximately 145 to 155 grain is for the 6.8 caliber cartridge comparable with the higher bullet weights of the 0.308 cartridge and is a good choice for a long range cartridge. The range of bullet weights is also above the popular 6.5 mm line. 
     The novel cartridge has a rim dimension to be adopted in actions chambered for the 0.308 Winchester. The body taper to 0.450″ diameter (P 2 ) is improved for operation in bolt action and self loading weapons. 
     The novel cartridge can be easily integrated in existing systems and magazine lengths adopted for the 0.308 Winchester. 
     As noted, the cartridge may be formed as a rimmed cartridge or as a rimless cartridge. The rimmed cartridge is provided for break up guns and combined guns. The remaining dimensions and data remain the same for the rimmed and rimless versions, except that slightly altered shoulder-powder room dimensions may be chosen. This applies, for instance, to lower pressure versions for break up guns. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a rifle cartridge, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of the specific embodiment when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a longitudinal sectional view taken through a schematic cartridge casing according to the prior art; 
         FIG. 2  is a diagrammatic side view of a rimless cartridge according to the invention shown with inch dimensions; 
         FIG. 3  shows the same cartridge in millimeter dimensions; 
         FIG. 4  illustrates a rimmed embodiment of the cartridge according to the invention; and 
         FIG. 5  shows the same cartridge in millimeter dimensions. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is seen a longitudinal section through a cartridge provided in order to clarify the nomenclature used herein. The illustrated cartridge is a rimless cartridge. Starting from the top, a bullet would be seated in a mouth  1  and a neck  2  would be crimped around the bullet in order to retain the same safely. The cartridge then widens via a shoulder  3 , which connects the neck  2  to a body  4 . Here, the body  4  is completely cylindrical, without a chamfer and therefore with a steady outer diameter from the shoulder/body transition to the bottom of the cartridge. As will be seen below, the novel cartridge (0.270 Schuster) has a slight conicity as it widens from the shoulder down to the base. 
     The body  4  is adjoined by a head  5 , which forms the base of the cartridge. The head  5  forms a belt  6  and a rim  7 . Even though the figure illustrates a rimless cartridge, there is still provided a rim  7 , which is formed due to an extraction groove  8  formed between the belt  6  and the rim  7 . A primer pocket  9  is formed centrally in the base of the head  5 . The primer pocket  9  connects via a vent  10  into a main chamber  12 . In this case, there is illustrated only a single vent hole, but it is possible for two or more to be provided. The vent  10  is defined by a web, which forms the wall between the primer pocket  9  and the chamber  12 . 
     Turning now to  FIG. 2 , there is shown an embodiment of the cartridge according to the invention. The cartridge is shown with a Spitzer bullet and an overall length of 2.800″, or 71.12 mm. This corresponds to the 0.308 Winchester and the standard 762 NATO round. The length of the cartridge shell is 1.924″ or 48.87 mm, which is considerably shorter than the 0.308 Winchester (51.18 mm). The length of the neck is 0.300″, or 7.62 mm, again shorter than the 0.308 Winchester (7.70 mm). 
     The cartridge shell is also referred to as a shell case. The length of the shell case, measured from the mouth to the very bottom wall, according to the illustrated embodiments is 48.87″ or 1.924 mm. The shell case length may be varied within a range of about 1.900″ to 1.950″ and formed for standard .270 caliber bullets. 
     The shoulder  3  of the novel cartridge is quite pronounced, as the shoulder walls enclose an angle of slightly more than 60 degrees. The corresponding angle of the 0.308 Winchester is slightly more than 40 degrees. That is, the imaginary apex of the shoulder  3  comes to lie just inside the neck  2  of the cartridge shell, at a distance of 1.8967″ or 48.177 mm from the base. The corresponding apex of the 0.308 Winchester comes to lie well ahead of the mouth  1 , at a distance of 56.46 mm from the base. 
     The bullet illustrated here is a Spitzer bullet which, with proper seating depth in the neck of the cartridge shell, results in an overall length of the cartridge of 71.12 mm. It will be understood that any of a plurality of other bullet shapes are available as well. The primer pocket  9  is sized so as to accept and properly seat a “large rifle” primer. 
     The following the tables compare the novel cartridge with the 0.308 Winchester cartridge loaded with the same bullet weights of 150 grains as an example. 
     The muzzle speed of the novel cartridge is 2,657 feet per second (fps) and 2,710 fps for the 0.308 Winchester cartridge. Both cartridges are at the same pressure level of 4.150 Bar (CIP). 
     These bullet speeds are calculated with “QuickLOAD Ballistic Program.” The speed data are an average formed from the 10 first listed loads from this calculation with different powders. The cartridges are loaded to approximately 85% of maximal pressure level. 
     The data in the tables are given in steps of 25 yards from zero to 1,000 yard distance. The data are calculated with SIERRA “Infinity Exterior Ballistics Software.” 
     150 grain Nosier bullets are used in these calculations as example. The spread differences to 145 or 155 grain bullets are similar and proportional with light differences. 
     In a variation of the novel shell case, there is provided a stronger neck diameter (H 1  and H 2 ) at approximately 0.315″ (8 mm). This prevents the cartridge from being loaded in smaller 6.5 mm caliber cartridges for security reasons. 
     Tables 1A and 1B show wind drift at 5 and 10 miles per hour light crosswind, respectively. Higher wind drift is proportional to this data. The novel cartridge features result in a lower wind drift. The novel cartridge is identified as “0.270 SCH” while the reference cartridge is identified as “0.308 WIN.” 
     
       
         
           
               
               
             
               
                 TABLE 1A 
               
             
            
               
                   
               
               
                 Range 
                 Wind Drift (Inches) 
               
            
           
           
               
               
               
            
               
                 (Yards) 
                 .270 SCH  
                 .308 WIN 
               
               
                   
               
            
           
           
               
               
               
            
               
                 25 
                 0.02 
                 0.03 
               
               
                 50 
                 0.09 
                 0.11 
               
               
                 75 
                 0.21 
                 0.25 
               
               
                 100 
                 0.37 
                 0.44 
               
               
                 125 
                 0.59 
                 0.7 
               
               
                 150 
                 0.86 
                 1.01 
               
               
                 175 
                 1.18 
                 1.39 
               
               
                 200 
                 1.55 
                 1.84 
               
               
                 225 
                 1.98 
                 2.36 
               
               
                 250 
                 2.47 
                 2.94 
               
               
                 275 
                 3.02 
                 3.6 
               
               
                 300 
                 3.63 
                 4.34 
               
               
                 325 
                 4.3 
                 5.15 
               
               
                 350 
                 5.04 
                 6.05 
               
               
                 375 
                 5.84 
                 7.03 
               
               
                 400 
                 6.72 
                 8.09 
               
               
                 425 
                 7.66 
                 9.25 
               
               
                 450 
                 8.68 
                 10.5 
               
               
                 475 
                 9.77 
                 11.85 
               
               
                 500 
                 10.93 
                 13.29 
               
               
                 525 
                 12.18 
                 14.84 
               
               
                 550 
                 13.51 
                 16.5 
               
               
                 575 
                 14.92 
                 18.26 
               
               
                 600 
                 16.41 
                 20.14 
               
               
                 625 
                 18.0 
                 22.13 
               
               
                 650 
                 19.67 
                 24.23 
               
               
                 675 
                 21.44 
                 26.46 
               
               
                 700 
                 23.3 
                 28.81 
               
               
                 725 
                 25.26 
                 31.29 
               
               
                 750 
                 27.31 
                 33.88 
               
               
                 775 
                 29.46 
                 36.61 
               
               
                 800 
                 31.72 
                 39.46 
               
               
                 825 
                 34.08 
                 42.44 
               
               
                 850 
                 36.54 
                 45.54 
               
               
                 875 
                 39.1 
                 48.76 
               
               
                 900 
                 41.78 
                 52.1 
               
               
                 925 
                 44.55 
                 55.55 
               
               
                 950 
                 47.43 
                 59.12 
               
               
                 975 
                 50.42 
                 62.79 
               
               
                 1000 
                 53.5 
                 66.56 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                 TABLE 1B 
               
             
            
               
                   
               
               
                 Range 
                 Wind Drift (Inches) 
               
            
           
           
               
               
               
            
               
                 (Yards) 
                 .270 SCH 
                 .308 WIN 
               
               
                   
               
            
           
           
               
               
               
            
               
                 25 
                 0.05 
                 0.05 
               
               
                 50 
                 0.18 
                 0.22 
               
               
                 75 
                 0.42 
                 0.49 
               
               
                 100 
                 0.75 
                 0.88 
               
               
                 125 
                 1.18 
                 1.39 
               
               
                 150 
                 1.72 
                 2.03 
               
               
                 175 
                 2.36 
                 2.79 
               
               
                 200 
                 3.11 
                 3.68 
               
               
                 225 
                 3.97 
                 4.71 
               
               
                 250 
                 4.95 
                 5.89 
               
               
                 275 
                 6.04 
                 7.21 
               
               
                 300 
                 7.26 
                 8.68 
               
               
                 325 
                 8.61 
                 10.31 
               
               
                 350 
                 10.08 
                 12.1 
               
               
                 375 
                 11.69 
                 14.06 
               
               
                 400 
                 13.43 
                 16.19 
               
               
                 425 
                 15.32 
                 18.5 
               
               
                 450 
                 17.35 
                 21.0 
               
               
                 475 
                 19.53 
                 23.7 
               
               
                 500 
                 21.87 
                 26.59 
               
               
                 525 
                 24.36 
                 29.69 
               
               
                 550 
                 27.02 
                 32.99 
               
               
                 575 
                 29.84 
                 36.52 
               
               
                 600 
                 32.83 
                 40.27 
               
               
                 625 
                 36.0 
                 44.25 
               
               
                 650 
                 39.35 
                 48.47 
               
               
                 675 
                 42.88 
                 52.92 
               
               
                 700 
                 46.6 
                 57.62 
               
               
                 725 
                 50.51 
                 62.57 
               
               
                 750 
                 54.62 
                 67.77 
               
               
                 775 
                 58.93 
                 73.22 
               
               
                 800 
                 63.44 
                 78.92 
               
               
                 825 
                 68.16 
                 84.87 
               
               
                 850 
                 73.08 
                 91.07 
               
               
                 875 
                 78.21 
                 97.52 
               
               
                 900 
                 83.55 
                 104.2 
               
               
                 925 
                 89.1 
                 111.11 
               
               
                 950 
                 94.86 
                 118.24 
               
               
                 975 
                 100.83 
                 125.58 
               
               
                 1000 
                 107.0 
                 133.13 
               
               
                   
               
            
           
         
       
     
     Table 2 shows the bullet drop. Although the novel cartridge starts at a lower speed and energy level, the trajectory of the cartridge is flatter for long range shooting. The bullet drop is better over approximately 350 yard distance and below with little difference. 
     
       
         
           
               
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Range 
                 Bullet Drop (Inches) 
               
            
           
           
               
               
               
            
               
                 (Yards) 
                 .270 SCH 
                 .308 WIN 
               
               
                   
               
            
           
           
               
               
               
            
               
                 25 
                 0.16 
                 0.15 
               
               
                 50 
                 0.63 
                 0.61 
               
               
                 75 
                 1.44 
                 1.39 
               
               
                 100 
                 2.59 
                 2.51 
               
               
                 125 
                 4.09 
                 3.98 
               
               
                 150 
                 5.97 
                 5.82 
               
               
                 175 
                 8.23 
                 8.05 
               
               
                 200 
                 10.89 
                 10.68 
               
               
                 225 
                 13.97 
                 13.74 
               
               
                 250 
                 17.48 
                 17.24 
               
               
                 275 
                 21.43 
                 21.21 
               
               
                 300 
                 25.86 
                 25.67 
               
               
                 325 
                 30.77 
                 30.64 
               
               
                 350 
                 36.19 
                 36.15 
               
               
                 375 
                 42.14 
                 42.23 
               
               
                 400 
                 48.64 
                 48.9 
               
               
                 425 
                 55.71 
                 56.2 
               
               
                 450 
                 63.38 
                 64.17 
               
               
                 475 
                 71.67 
                 72.82 
               
               
                 500 
                 80.62 
                 82.21 
               
               
                 525 
                 90.24 
                 92.37 
               
               
                 550 
                 100.57 
                 103.35 
               
               
                 575 
                 111.65 
                 115.17 
               
               
                 600 
                 123.49 
                 127.91 
               
               
                 625 
                 136.14 
                 141.59 
               
               
                 650 
                 149.64 
                 156.27 
               
               
                 675 
                 164.02 
                 172.02 
               
               
                 700 
                 179.32 
                 188.87 
               
               
                 725 
                 195.58 
                 206.9 
               
               
                 750 
                 212.84 
                 226.16 
               
               
                 775 
                 231.16 
                 246.71 
               
               
                 800 
                 250.57 
                 268.62 
               
               
                 825 
                 271.12 
                 291.97 
               
               
                 850 
                 292.87 
                 316.8 
               
               
                 875 
                 315.86 
                 343.2 
               
               
                 900 
                 340.16 
                 371.22 
               
               
                 925 
                 365.8 
                 400.95 
               
               
                 950 
                 392.85 
                 432.43 
               
               
                 975 
                 421.36 
                 465.75 
               
               
                 1000 
                 451.4 
                 500.95 
               
               
                   
               
            
           
         
       
     
     Table 3 shows the bullet speed and energy. Although the novel cartridge starts at a lower speed and energy level, the speed and energy are superior over approximately 125 yard distance and below with little difference. 
     
       
         
           
               
               
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 .270 SCH 
                   
                 .308 WIN 
               
            
           
           
               
               
               
               
               
            
               
                 Velocity  
                 Energy 
                 Range 
                 Velocity 
                 Energy 
               
               
                 (ft/sec) 
                 (ft/lbs) 
                 (Yards) 
                 (ft/sec) 
                 (ft/lbs) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 2657.0 
                 2350.9 
                 0 
                 2710.0 
                 2445.7 
               
               
                 2608.9 
                 2266.6 
                 25 
                 2651.6 
                 2341.4 
               
               
                 2561.4 
                 2184.8 
                 50 
                 2594.0 
                 2240.7 
               
               
                 2514.3 
                 2105.2 
                 75 
                 2537.1 
                 2143.6 
               
               
                 2467.7 
                 2027.9 
                 100 
                 2480.9 
                 2049.6 
               
               
                 2421.6 
                 1952.8 
                 125 
                 2425.4 
                 1958.9 
               
               
                 2376.0 
                 1879.9 
                 150 
                 2370.5 
                 1871.3 
               
               
                 2330.8 
                 1809.2 
                 175 
                 2316.4 
                 1786.9 
               
               
                 2286.2 
                 1740.5 
                 200 
                 2263.0 
                 1705.4 
               
               
                 2242.0 
                 1673.9 
                 225 
                 2210.3 
                 1626.9 
               
               
                 2198.3 
                 1609.2 
                 250 
                 2158.2 
                 1551.1 
               
               
                 2155.0 
                 1546.5 
                 275 
                 2106.8 
                 1478.9 
               
               
                 2112.3 
                 1485.8 
                 300 
                 2056.2 
                 1407.9 
               
               
                 2070.0 
                 1426.9 
                 325 
                 2006.3 
                 1340.4 
               
               
                 2028.2 
                 1369.9 
                 350 
                 1957.1 
                 1275.5 
               
               
                 1986.9 
                 1314.7 
                 375 
                 1908.6 
                 1213.1 
               
               
                 1946.2 
                 1261.3 
                 400 
                 1860.9 
                 1153.2 
               
               
                 1905.9 
                 1209.7 
                 425 
                 1814.0 
                 1095.8 
               
               
                 1866.2 
                 1159.8 
                 450 
                 1768.0 
                 1040.9 
               
               
                 1827.1 
                 1111.7 
                 475 
                 1722.8 
                 988.4 
               
               
                 1788.5 
                 1065.2 
                 500 
                 1678.5 
                 938.2 
               
               
                 1750.5 
                 1020.4 
                 525 
                 1635.2 
                 890.4 
               
               
                 1713.1 
                 977.3 
                 550 
                 1592.8 
                 844.9 
               
               
                 1676.4 
                 935.9 
                 575 
                 1551.5 
                 801.6 
               
               
                 1640.3 
                 896.0 
                 600 
                 1511.2 
                 760.5 
               
               
                 1604.9 
                 857.7 
                 625 
                 1472.1 
                 721.7 
               
               
                 1570.2 
                 821.0 
                 650 
                 1434.2 
                 684.9 
               
               
                 1536.2 
                 785.8 
                 675 
                 1397.4 
                 650.3 
               
               
                 1502.9 
                 752.2 
                 700 
                 1361.9 
                 617.7 
               
               
                 1470.5 
                 720.1 
                 725 
                 1327.8 
                 587.1 
               
               
                 1438.9 
                 689.4 
                 750 
                 1295.1 
                 558.6 
               
               
                 1408.1 
                 660.2 
                 775 
                 1263.9 
                 532.0 
               
               
                 1378.2 
                 632.5 
                 800 
                 1234.2 
                 507.3 
               
               
                 1349.1 
                 606.1 
                 825 
                 1206.2 
                 484.5 
               
               
                 1321.1 
                 581.2 
                 850 
                 1179.8 
                 463.5 
               
               
                 1294.0 
                 557.6 
                 875 
                 1155.1 
                 444.3 
               
               
                 1268.0 
                 535.4 
                 900 
                 1132.0 
                 426.8 
               
               
                 1243.0 
                 514.5 
                 925 
                 1110.6 
                 410.8 
               
               
                 1219.1 
                 495.0 
                 950 
                 1090.8 
                 396.2 
               
               
                 1196.4 
                 476.7 
                 975 
                 1072.5 
                 383.1 
               
               
                 1174.9 
                 459.7 
                 1000 
                 1055.5 
                 371.0 
               
               
                   
               
            
           
         
       
     
     The term “substantially” as used in the claims is to be understood with reference to the respectively modified measurement or numerical value. The term varies and allows a modification of the associated value by a maximum of 3 to 6%. Where the modifier is not used in the context, the allowed variation is with the acceptable error range as understood by those of skill in the art and will, typically, lie in the 1-2% range.