< Previous142 PISTOLS, RIFLES AND MACHINE GUNS Fig. 65.—The 7 mm. Enfield rifle, firing position. WWW.RIFLEMAN.ORG.UKR 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need for an exposition of the salient factors involved, were from misinformed enthusiasts whose opinions were based on out-of-date concepts.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 factors WWW.RIFLEMAN.ORG.UK1 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, and WWW.RIFLEMAN.ORG.UKRIFLES 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. T H E F . N . R I F L E The F.N. factory in Belgium has produced a post-war design of automatic rifle with provision for semi-automatic action. The weapon appears to be based on one of Browning's designs; it is conventional in appearance with a wooden fore-end and butt. A short overall length has been obtained by fitting a short barrel, and the gas cylinder is mounted above. The magazine is underneath and in front of the pistol grip. A conventional aperture sight is fitted. The rifle weighs about eight pounds and has a simple mechanism, but if the usual 24 inch barrel were fitted it would be about the same length as the No. 4 Rifle. T H E . 3 0 i n . M . I G A R A N D R I F L E Much has been heard about this rifle recently, and as the Americans are naturally enthusiastic about it, a brief impartial review ^vill set it in correct perspective. The M.l Garand rifle (Figure 63), adopted by the U.S.A. army in 1936, was being developed and underwent trials during the preceding five years, and is therefore about twenty years old today. This is not a great age for a rifle; models do not change with the same rapidity as they do in the motor trade, but the intervention of a major war always accelerates the advancement of weapons. By present day standards the Garand is rather bulky and heav)' (9J pounds) and has no provision for automatic fire. As it fires an exceptionally powerful cartridge the recoil is fairly heavy, and it is doubtful if it would be controllable firing automatically. The magazine is charged with an eight-round clip, which necessitates recharging too frequently to take full advantage of the semi-automatic action, and there is also a tendency to j am when recharging in a hurry. The magazine platform is connected with the piston extension spring and has an undesirably complex mechanism. Tests have shown that the Garand rifle can fire 35 rounds per minute when the 7 mm. Enfield and the German F.G.42 Paratroop's rifle each fire 60. A further disadvantage of the Garand is the additional move ment at the firing position due to the need for re-loading after every eight shots—as all soldiers know movement draws fire. The enormous superiority of rifles with twenty round magazines is here demonstrated. The Garand is fitted with an ordinary aperture sight, which, although cheaper than a telescope, is greatly inferior. The M.2 cartridge is more powerful than is necessary for a rifle at the shorter ranges where the striking energy is high in any case, and the consequent recoil velocity WWW.RIFLEMAN.ORG.UKj ^ g 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 is hieh enough to be unpleasant; this would have to be accepted were it necessary but it is not. At the longer machine gun ranges the bullet has less enerev than the .303 in. Mk. 7 bullet, due to its inferior ballistic coefficient Tliis fact has been proved by trials. The M.2 bullet has a muzzle velocity of 2800 feet per second, and a weight of 152 grains. Long range machine gun performance has been sacrificed for greater striking energy at the short ranges, and there seems to be no valid reason for this—it is not the bang that kills. The conclusion is that the USA Army prefers striking energy at short ranges to machine gun performance at the longer ranges, and is prepared to accept the greater recoil energy and consequent additional difficulty of training men to fire accurately with the rifle. There seems to be no doubt that a lower energy bullet is preferable if it does the job, and trials have proved that the .280 in. bullet is completely adequate in all respects. A COMPARISON BETWEEN BOLT ACTION AND SEMI-AUT OMA TIC RIFLES The object of this section is to see how an army will benefit by adopt ing a semi-automatic rifle in place of an orthodox one. Continual practice is necessary to enable a soldier to fire fifteen rounds per minute with a bolt action rifle, because of the faultless manipulation of the bolt that is needed, and the frequent recharging of the magazine with five round charo-ers or clips. The movements of the filer's hand are as follows; preS the trigger, move from the butt to operate the bolt, return to the small of the butt (index finger on the trigger), re-align the sights on the target, and press the trigger. Much practice is necessary to keep the butt firmly in the shoulder when the rifle is held only with the left hand, and it is evident that the right hand moves a good deal. The record for rapid fire with an S.M.L.E. rifle stands at about 36 rounds in one minute, and it was set up by an instructor at the Small Arms School, Hythe, which has now become a wing of the School of Infantry. Such high rates of fire are only attainable for ashort time and after much practice; 15 rounds per minute is a fair figure for a trained soldier firing with a prac tical degree of accuracy in the field. Even this rate will drop after a few minutes, or if it does not the degree of accuracy will, owing to fatigue. A semi-automatic rifle performs all the actions that the soldier had to do with his hand, therefore, both hands can now be kept on the rifle during the firing of a magazine. The interval between shots is far shorter, the movement which attracts fire is eliminated, fatigue is reduced, ancl the sights remain roughly aligned on the target. A soldier should be able to fire about 40 shots in a minute with, at least, the same standard of accuracy as hitherto. Less practice is required to maintain the standard because there is no bolt manipulation, and magazine changing is substituted for re-charging by clip. Experienced marksmen have fired more than 60 aimed shots in a minute with a semi-automatic rifle. It may appear that undue emphasis has been placed on rapidity of fire, and that the problem may well be one of preventing the soldier from finishing his ammunition too soon. The last is an important consideration that will have to be overcome by training; but remember WWW.RIFLEMAN.ORG.UKR I F L E S 1 4 7 the B.E.F. in 1914. Superiority of fire is essential in war, and once the enemy have passed through the defensive fire of a position and have only 200 or 300 yards to go, small arms alone must stop them._ Whenever time permits obstacles are always placed in front of a defensive position to delay the enemy and give the defenders more time to kill. This is the period when rapid fire'is most effective. Instances have occurred in Korea where positions have been overrun by weight of numbers and nothing else—the massed attack. The real solution is machine guns, but the urgent need still remains for small units to be able to concentrate a large volume of fire on their immediate enemies be it attack or defence—the semi-automatic rifle supplies the means to do this. By way of conclusion let us compare two Infantry sections and see what their maximum rate of rapid fire is likely to be. In war the section seldom has more than one N.C.O. and say six men, and their armament is 1 L.M.G., 2 machine carbines, and 4 rifles. The machine carbines will be disregarded on account of their short range; they should be employed only at the last when the enemy is less than 100 yards away. Taking one minutes rapid fire as the basis the results will be: 1 L.M.G. at 90 rd. p.m 90 rounds 4 r i fl e s a t 1 5 r d . p . m " To t a l . . • • 1 5 0 „ 1 L.M.G. at 90 rd. p.m. ■• •• 00 „ 4 semi-auto rifles at 40 rd. p.m. . • 1"0 „ To t a l . . • • 2 5 0 „ The difference is impressive, and supposing the semi-automatic riflemen are not trained up to 40 rounds per minute but only achieve 30; the section will still produce 210 rounds per minute, or an increase o v e r t h e r i fl e s e c t i o n o f 4 0 % . a One other aspect requires noting and this is the mci eased complexity of the mechanism. A semi-automatic rif^e will cost "J" ordinary rifle, and the teaching of the mechanism will be a little moie difficult, but there is already the light machine gun previously stated, there is no fundamental mechanical difj^eience between the two weapons. The soldier has been equipped with a far more efficient rifle, and will be able to use it than hitherto. Here is a not uncommon example of an mciease m weapon complexity leading to a reduction m training time, combined with a better performance. R I F L E B A R R E L S The Chamber and Bore Figure 66 is a drawing of a .303 in. 'chamber; the mam parts are named. The small cone is sometimes known as shoulder and t chamfer is the reduction in diameter from the mouth of the case to beginning of the leed. * in connection with bullets. PRM—L WWW.RIFLEMAN.ORG.UK1 4 8 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 The leed is the region where the smooth bore section, to clear the bullet, is built up to the full form of the rifling. Its task is to guide the bullet truly into the rifling, ensuring accurate engraving without wobble or other de-stabilising influence. Complete obturation should be effected at this point to prevent excessive erosion which exercises an adverse Brccch Foce Uorg# Con® Smo \ Fig. 66.—The chamber for the .303 in. S.M.L.E. rifle cartridge. influence on accuracy of fire. The bullet manufacturer must be given a tolerance on the bullet diameter for mass production, and this is generally about 0.002 inch. Similarly a tolerance of about 0.003 inch is allowed on the bore diameter. The .303 in. ball bullet has a high diameter of 0.312 inch, which is designed to approximate to the low groove diameter of the barrel. In practice there is usually a small clearance between the bullet and the groove, but this is of no consequence w h e n d e f o r m a b l e b u l l e t s a r e u s e d . The .303 in. Mk. 7 ball bullet has a lead core and a harder envelope of gilding metal, cupro-nickel, or mild steel with a rolled on coating of one of the first two metals. The core provides the density, and the Fig. 67—Set up of a .303 in. Mk. 7 bullet. envelope the strong container to prevent break-up. The chamber pressure is of the order of 18 tons per square inch, and this force on the base of a deformable bullet causes it to set up into the grooves and barricade the young gas. During ammunition production bullets are tested from time to time to ascertain their ability to set up correctly. They are fired from a rifle which has had the barrel cut down near to the leed. The high pressure, combined with the early cessation of sup port from the barrel causes the bullet to set up in the manner shown in Figure 67. The flange is about 0.40 inch in diameter, and should be WWW.RIFLEMAN.ORG.UKRIFLES 149 regular with no splitting. A few bullets are fired at short range into a long box filled with cork dust, and then recovered by sifting. Set up compensates for leed wear and allows a reasonable barrel life, for a barrel is no better than its leed. Once the young gas is able to pass the bullet in the leed it squashes it, which action is kno-wn as wire drawing. Engraving cannot take place, so the bullet emerges unspun and unstable. In peace time cleaning often wears out rifle barrels, but it is the leed of a machine gun barrel that determines its life, because of the high temperature generated by automatic fire. The lands (ribs) become progressively flatter until they fail to spin the bullet, which is driven along at a rapidly increasing velocity until it meets better lands; but by then the velocity is so high that considerable skidding occurs and the surface of the envelope is machined oflF as the bullet tries to rotate. The result is a gross degree of under-spin which allows the bullet to yaw. Such shots make oval holes in a target screen and are called "tippers." If further firing is carried out the degree of yaw increases until the bullet flies broadside on and is known as a "BSO." The expression "keyhole" is also used, but is not common in the technical service. The armour piercing bullet is rigid and will not set up. It is larger in diameter than a ball bullet and is engraved by brute force. The A. P. bullet has a hard steel core surrounded by a thin lead sheath which is encased in a mild steel envelope coated with gilding metal or cupro- nickel. Some types omit the lead sheath and use a thicker envelope; in this way the core weight is increased to give an improved penetration performance. A.P. ammunition causes more barrel wear than ball because of the larger diameter and unyielding construction; further more the lack of set up leads to failure of accuracy in a barrel which still fires ball satisfactorily. The A.P. bullet is rigid enough to resist wire drawing by gas escaping past it, but fails when the lands in the first part of the barrel are worn down and engraving is inadequate unless set-up occurs. A substantial improvement in the ballistic coefficient is obtained by streamlining, or tapering, the rear part of a bullet, but set up cannot occur. For this reason the barrel life is shortened, and a good leed is essential. A cool propellant has to be used to reduce erosion of the leed. Difficulty often arises because a cool burning powder bulks larger than a hotter one, and there is not always room in the case for the requisite charge. The bore is responsible for accelerating the bullet up to the specified muzzle velocity, and discharging it in a predetermined direction. The length of a barrel is a compromise between the ballistic requirement and the user's specification, but the charge must be all burnt well within the barrel. Too short a barrel gives an objectionable report and flash. Rifling The more common forms of rifling used in small arms are depicted in Figure 68. During the black powder era every conceivable type of rifling was tried, including a hexagonal bore designed by Whitworth. Finally the Metford form was adopted in the Lee-Metford rifle; the shallow arc- WWW.RIFLEMAN.ORG.UK1 5 0 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 shaped grooves spun the soft projectiles well, and were easy to clean—■ an essential feature when using black powder which produced much fouling. With the introduction of Mark 1 Cordite the Metford grooves wore out quickly owing to the erosive nature of the new propellant, and it was soon discovered that shallow concentric grooves with sharp edges lasted much longer. Crudely speaking it was mostly a matter of more metal taking longer to wear away. A practical design of bullet is, unfortunately, inherently unstable unless it is given a high rate of spin. The conditions of use dictate a strong base to withstand the gas pressure, and a pointed nose to improve the ballistic coefficient, thus the centre of gravity is displaced towards the base. The centre of pressure then falls in front of the centre of gravity, whereas the reverse should be the case for stable unspun flight—for example the ordinary dart or arrow. The rate at which a projectile is spun depends on many complex factors, amongst which are: the moments of inertia (distribution of mass within the body), the muzzle velocity, and the density of the medium in which the projectile moves. If the mass distribution is unfavourable to stability the rate of spin has to be increased, and it must also be increased as the muzzle velocity rises. The density of the medium, air, in which the projectile moves remains reasonably constant from a practical point of view, but corrections are given in machine gun talales for firing at high altitudes. Rifling ensures that a bullet leaves the bore:— With the required radial velocity. With its axis coincident with that of the bore. Spinning accurately about its axis. With its centres of gravity and pressure lying on this axis. The nature of the rifling depends on the construction of the bullet and the type of weapon. Barrels intended for pistol ammunition have narrow lands and broad grooves in order to reduce the shot start pressures. A narrow land cutting into a bullet envelope exercises less drag than a broad one. Pistols and machine carbines work at com paratively low pressures, and the importance of low shot start pressures will be appreciated for revolvers and blow-back operated semi-auto matic pistols. A bullet is subjected to severe stresses by rifling and suffers some distortion, which is reduced when the lands are narrow, con sequently where accuracy is of paramount importance, such as in a rifle, narrow lands are often found. However, they wear out quicker than broad ones, and are not found in machine guns which, firing automatically, impose a high rate of wear, and are usually fitted with lands and grooves of equal width. Modern rifling is difficult to classify owing to the variations, but two distinct kinds are in being: Enfield and Continental or Springfield. The former is characterised by having an odd number of grooves which are the same width as the lands, whilst the latter has an even number that are broad with respect to the lands. Enfield rifling is cut one groove at a time, the tool being backed up by the opposite land. Although this appears a slower method than the Springfield, where the cuts can be taken in pairs, the finish is much better because the tool is steadier WWW.RIFLEMAN.ORG.UKRIFLES 151 and consequently the lapping time to finish the bore is less. The Bren and Besa (air-cooled) guns are of Continental origin, and have relieved grooves which are intended to reduce the engraving stresses, but the Fig. 68—Rifling. symmetrical formation to present plenty of metal is noticeable (Figure 68). Radial rifling is difficult to cut and is seldom encountered. The depth of rifling grooves is dependent, to some extent, on the role of the barrel and the eonstruction of the bullet. Shallow grooves cause little bullet distortion and are suited to rifles; whilst deep grooves are better for machine gun barrels, although the bullet envelope is cut more deeply, and consequently has an inferior ballistic finish. British weapons of rifle calibre show no appreciable difference in groove depth, and are standardised to a mean figure of approximately .006 ineh; but the U.S.A. prefers a figure of about .004 inch. It should be noted in this connection that the British bullet is deformable, and the Ameriean, rather less so; the respective rifling systems therefore match the bullet construction. All other things being equal, the British combination will give the longer barrel life. Uniform pitehed rifling is standard for small arms. Rifles and machine guns generally have one turn in about ten inches, whereas weapons firing pistol cartridges have an easier twist of about one in 14 to 16 inches. For comparative purposes it is best to express the twist in calibres, thus the .303 in. barrel has one turn in 10 inches or one in 33 calibres. (The Mk. 7 bullet is spinning at a rate of 2930 revs. p. sec. at the muzzle.) The direction of twist is immaterial, it is a matter of custom. British small arms are rifled left-handed, that is anti-clockwise as seen from the breech, but the U.S.A. and.the Continent employ right-handed rifling. There are numerous exceptions. British weapons of Continental origin have retained the Continental direetion; examples are: the Lewis and Besa machine guns, and the Sten machine carbine which, although a WWW.RIFLEMAN.ORG.UKNext >