THE 7mm. (.280 in.) ENFIELD RIFLE The needs of security must be served at the time of writing, so it is only possible to summarise the information that has already been released, together with a few remarks of a general charaeter, on automatic rifles. The automatic rifle is not a new weapon. Hirain Maxim made one in 1884, and the Americans and Russians both introduced one into their armies about 1936, whilst Germany began in 1941, and produced several models in the next three years. Attempts were made in this country, during the first World War, to convert the No. 1 Rifle to semi automatic action. Some specimens still exist and, although rather clumsy, show the same fundamental characteristics as the modern article. The calibre of the new rifle has been allotted the official nomen clature of 7 mm., but it is more convenient to use inches when com paring with other calibres known in inches. Construction A photograph of the rifle is shown in Figure 63. Modern warfare demands a lighter weapon than has been used in the past; the weight of the 7 mm. rifle is about 84 pounds. The rifle and cartridge have been especially designed for a specific purpose and include the best features selected from other weapons. The .303 in. cartridge is 3 inches long and the 7 mm. has been reduced to 24 inches; the reduction allows a shorter feed stroke and assists in shortening the overall length of the rifle. The bullet weight is 140 grains and the muzzle velocity is 2530 feet per second. The illustration shows that a straight-through design has been adopted together with a telescopic sight mounted at a convenient height. The sight mounting has been built in the form of a carrying handle so that the telescope is automatically protected to some extent. It has unit magnification which in addition to eliminating all focussing difficulties (see Chapter 8, telescopic sights), allows a good view of the field of fire. Iron sights are provided in case the telescope is damaged. There is no dead wood in the butt, the interior being fully occupied. The fore-end is made of wood and has a full left-hand grip to prevent the fingers reaching the hot gas cylinder; incidentally the grip provides an excellent142 PISTOLS, RIFLES AND MACHINE GUNS Fig. 65.—The 7 mm. Enfield rifle, firing position.R I F L E S 1 4 3 hand hold for both shooting and bayonet fighting. The position of the breech is indicated by the front edge of the magazine and shows that the barrel is of normal length for the calibre, in spite of the short length of the rifle. The position of the twenty round magazine ensures that its weight is in the optimum place near the shoulder. There is no waist to the butt, as in conventional rifles, so a pistol grip has been fitted in a convenient location for the right hand, and a linkage operates the trigger. The safety catch is mounted in the front part of the trigger guard and is similar to that on the Garand rifle; it is operated by the back of the index finger. The weapon handles well in all firing positions, including the waist. Figure 65 is a photograph of the rifle in action. A Comparison between .280 in. and .30 in. Calibres During the summer of 1951, when information concerning the 7 mm. rifle was first released, there was a lot of correspondence in the daily press which showed the interest of the country in its new iveapons of defence. Many of the letters, clearly emphasising the need for an exposition of the salient factors involved, were from misinformed enthusiasts whose opinions were based on out-of-date concepts. There is no doubt in the minds of the people whose task it is to study these matters that a semi-automatic rifle is a vastly superior Infantry arm compared with an orthodox rifle. A. comparison is draivn in a later section. The main point about which discussion centred, however, was the calibre of .280 in. Many of the eager scribes contended that it was too small, and this opinion appears to be shared by the U.S..A. Let us settle this point as far as is possible without contravening security. The real weapon is the bullet, for it is this that strikes the enemy, and the rifle is the projector which discharges the bullet in a known direction, at a known velocity, and at a predetermined angle of elevation, depending on the range. It follows that the first item to design is the cartridge containing the bullet and propelling charge. Now the army requires one type of cartridge for its rifles, light machine guns, and medium machine guns, in order to keep the supply problem within practical limits; therefore the bullet will have to be effective at the extreme range of the longest range weapon—the medium machine gun. Suppose this range to be 2500 yards. What is the target? Probably a man wearing normal uniform and field equipment. The bullet must pene trate his body sufficiently to inflict, at least, a severe wound, but it must not be excessively powerful because the recoil velocity of the rifle has to be kept down, and this is dependent on the momentum of the pro jectile. Furthermore, powerful cartridges require heavy rifles to absorb the recoil energy. The ranging ability of a projectile depends on its ballistic coefficient, which in turn depends mainly on the shape, stability, and the ratio of weight to cross sectional area. (A golf ball has a better ballistic co efficient than a ping-pong ball—try throwing them.) The numerical value of the ballistic coefficient should be as high as possible. A small cross-sectional area will suffer less air resistance than a large one, and in addition a bullet should have the greatest possible density; these factors1 4 4 P I S T O L S , R I F L E S A N D M A C H I N E G U N S dictate a long thin bullet, but stability limits the length. The .280 in. bullet weighs 140 grains, and the M.2 of the Garand rifle, 150 grains. For the purpose of drawing a rough comparison no great error will accrue if the two bullets are deemed to have the same weight. In this case, all other things being even, the .280 in. bullet will have the better ballistic coefficient. Discharge both at the same muzzle velocity and their respective momenta will be equal, so if the two rifles are also of equal weight, they will have much the same recoil velocities for all practical purposes. The energy of the bullets is found from the formula: \mv^, where m is the mass, and v the velocity. Both bullets have been given the same mass and muzzle velocity, and will therefore have identical muzzle energy, but the .30 in. bullet with its inferior ballistic coefficient will lose velocity along the trajectory more rapidly than the .280 in. bullet. Thus, after leaving the muzzle the striking energy of the .30 in. bullet will deteriorate more rapidly than that of the .280 in. bullet. All that can be said in favour of the larger calibre is that it will make a larger hole in the target, but the penetration of the higher velocity smaller projectile will be greater. At the longer machine gun ranges the .280 in. bullet will be much superior in striking energy and also the flatter tra jectory assists in compensating for errors in range estimation. Even if the velocity of the .30 in. bullet is raised by, say, 200 feet per second, it will still be inferior at the longer machine gun ranges, so great is the advantage of a good ballistic coefficient. Of course the .30 in. bullet could be given a comparable performance by increasing its weight to improve the ballistic coefficient, but then the muzzle momentum would also increase, and with it the recoil velocity of the rifle. Nothing is gained by over-hitting, or in everyday language: why take an axe when a dagger will do the job? The two big advantages of a low recoil velocity may be stated now. The first is the greater facility with which men can be trained up to a given standard of proficiency. A heavy recoil velocity makes many men gun-shy, and in consequence they flinch as they fire and the degree of accuracy is poor. The second is a lessening fatigue during prolonged fire. The reduction of cross sectional area cannot be taken too far, .280 in. is about the lower limit, bearing in mind the performance required. For instance a .22 in. bullet would have too low a ballistic coefficient to give a satisfactory performance because it is not possible to obtain the necessary weight in this small calibre. Perhaps this brief excursion into external ballistics will "debunk" some of the nonsense that has been published regarding the .280 in. calibre. The treatment is necessarily incomplete but, factually, it is based on sound reasoning. The reader may also recall that in the last war both the Italians and the Japanese used 6.5 mm. (.25 in.) rifle and machine gun cartridges, and that the adoption of a .276 in. calibre was being considered in this country in 1913. To sum up: there is nothing new in the adoption of a smaller calibre than .303 in.; ballistitians have long realised that a light rifle can only be achieved by a reduction in the muzzle energy of the bullet, andRIFLES 145 further, that a correctly designed small calibre bullet is adequate for both rifles and machine guns. Since the case has been established for a light rifle (8-f pounds) with a low recoil velocity (under 10 feet per second) a compromise must be accepted, and there are excellent grounds for believing that the .280 in. rifle and cartridge are the best possible solution to the problem. It seems that the only way of comdncing the hard-boiled sceptics would be to invite them to stand at the extreme range of the bullet and submit to a peppering by machine gun fire—I doubt if they rvould have the courage of their convictions.Next >