MILITARY CARTRIDGE RELATIONSHIPS
© A G Williams
This is based on an article which first appeared in "Guns Review" magazine in April 1994, but has been much modified and extended.
It is taken for granted that whenever a new commercial rifle or pistol cartridge is introduced, it will probably be a derivative of an existing round. The 7x57 Mauser, .30-06 and .375 Holland & Holland Belted Rimless Magnum Nitro Express (to give it its formal title) have all parented huge families of variations in calibre, length or shape and are still doing so today. If a cartridge is genuinely new, such as the 10mm Auto, it is likely to find itself rapidly shortened (.40 S&W), lengthened (10mm Magnum) or otherwise molested in the interests of achieving some marginal advantage.
In contrast, military cartridges are rarely interfered with in this way. They are developed with little regard to cost for a specific purpose and once adopted remain unaltered for decades. However, there are well-known exceptions; the 7.92x57 was shortened to make the 7.92x33 Kurz cartridge for the WW2 German MP 43/44/StG 44 assault rifles, and the American .30-06 (7.62x63) was shortened to make the 7.62x51 NATO. Perhaps more surprising is that the 5.56mm NATO was developed from a commercial small-game cartridge - it's usually the other way round.
There have also been some heavy machine gun and cannon cartridges which were derivatives of existing service rounds and these are the subject of this article. Some of these are well known, others less so and some are quite surprising. The following groups of cartridges are illustrated by attached photos - just click on the links.
Group 1: Based on the .50" Browning.
This consists of the first five cartridges in this PHOTO, which are (from right to left): .50" Browning (12.7x99), 13.2mm Hotchkiss (13.2x96; also 13.2x99 and 13.2x93 are also found), .50.30 AP test (7.62x99), 10mm XM277 (10x107), .50 Spotter (12.7x76).
The .50" Browning was among the first of the heavy machine gun rounds, being introduced shortly after the First World War. During the interwar period a number of competitors emerged, of which the only survivor is the Soviet 12.7x108 round.
One which achieved considerable success at the time, being adopted by the French, Italian and Japanese (among others) was the 13.2mm Hotchkiss. The gas-operated gun was completely different from the recoil-operated Browning but the cartridge was remarkably similar in all dimensions except for calibre; in fact only an expert can distinguish them without having them side by side. The Italians designed the Breda M31 AFV gun around the cartridge. Even the Browning M2 aircraft HMG was chambered for this cartridge, by FN of Belgium and by the Japanese Navy Air Force, who called it the 13mm Type 3.
A more significant modification was made in Britain, which not only involved necking the case up to 13.9mm but also adding a belt, to create the .55" Boys anti-tank rifle cartridge (not shown in this photo).
The .50.30 looks remarkably similar to the German Patrone 318 (7.92x94) cartridge for the PzB anti-tank rifles, but it was only developed for testing AP bullets at high velocity.
The 10mm XM277 was developed in the 1960s for the GAU-6 rotary gun, apparently intended as a helicopter weapon. The cartridge reportedly generated a muzzle velocity of 4,000 fps (1,220 m/s). It might make the basis for a good long-range varmint rifle - if varmints ever grow to elk size! The gun was later modified to revert to .50 cal. Incidentally, it bears no relationship to the current GAU-19/A apart from the rotary configuration.
With the introduction of large-calibre recoilless anti-tank guns in the 1950s, it was decided that the simplest way of ensuring a hit with these low-velocity shells was to fit the gun with a ballistically matched spotting rifle firing bullets with a "flash" compound in the nose. The gunner fired the spotting rifle until a hit on the target was observed, at which point the heavy ordnance was triggered. There was much experimentation to develop the best cartridge for this purpose, but the most successful was achieved by simply shortening the .50" heavy machine gun round. Both large RCL cannon and spotting rifles are now obsolete; the former replaced by guided missiles, the latter by laser rangefinders. The .50" Browning soldiers on!
Group 2: Based on the 20mm Hispano.
This consists of the next three cartridges in the same PHOTO: 20mm Hispano-Suiza HS 404 (20x110), .50" High Velocity (12.7x120), 15mm FN-BRG (15x115).
The French-designed 20mm Hispano was the classic RAF fighter weapon for most of WW2 (and a decade thereafter).
The Americans made some use of it, but were always more interested in muzzle velocity, so they couldn't resist necking the case down to .50 calibre to create the .50HV. This effort remained experimental.
Nearly half a century later, FN were seeking to develop a more powerful replacement for the .50" Browning, better able to penetrate light armoured vehicles (in effect, a Western equivalent to the Soviet 14.5mm KPV). FN initially selected the 20mm Hispano case as a basis and necked it down to 15mm. The weapon and its ammunition had a protracted development and finally emerged as a 15.5mm, as we shall see.
Group 3: Based on the 14.5mm ATR.
The final group of three cartridges in this PHOTO: 14.5mm PTRD/PTRS/KPV (14.5x114), 23mm NS-23, NR-23, AM-23, GSh-23, GSh-6-23 (23x115), 15.5mm FN BRG (15.5x106),
The Soviet 14.5mm cartridge was developed for anti-tank rifles in 1939, since an earlier effort in 12.7mm caliber had proved inadequate. The PTRD and PTRS rifles were formidable performers, among the best of the WW2 ATRs. After the war, the cartridge was adopted for the KPV heavy machine gun, still by far the most powerful in its class.
Before the end of WW2, the case was selected for a new aircraft gun, the NS-23, and modified by the simple expedient of necking it out to accept the 23mm shells from the VYa-23 already in service (which fired a much more powerful 23x152B cartridge). The 23x115 cartridge, in modified form, is still in service today.
The 15.5x106 was FN's final effort to make a KPV competitor, appropriately by necking out the KPV's case, While it seemed to work well enough, it never found any customers and effectively bankrupted the company. Not surprising, really; anyone wanting a gun in that class could have bought the KPV for a lot less cash.
Group 4: Based on the MG 151.
The first four in this PHOTO: 15mm MG 151 (15x96), 20mm MG 151/20 (20x82), 20mm Ho-5 (20x94), 20mm Hispano (20x110).
The first two form one of the best known pairings. Early in World War 2 the Luftwaffe introduced an excellent new gun, the Mauser MG 151, firing a 15mm high-velocity cartridge. Good as it was, a clamour for more destructive power arose and led to the case being necked out to form the 20mm MG151/20 round. The extra HE capacity was considered well worth the loss in muzzle velocity and the larger cartridge virtually replaced its predecessor. Modified versions of the 20mm gun and cartridge are still in production in South Africa, under the designation Vektor GAl.
During WW2, the Japanese Army Air Force made some use of the MG 151/20, but also developed their own gun, the Ho-5 (ironically based on the Browning M2) in 20x94 calibre, which appears to be a stretched MG 151.
The Hispano can't have been a copy since it emerged slightly earlier; on the other hand it is unlikely that the MG 151 copied the Hispano case as it was already under development when the HS 404 emerged blinking into the light of day, but you never know…it is certainly an interesting coincidence that the rim and case diameters are virtually identical. A possible explanation is the previous existence of the 20x105B cartridge for the interwar Solothurn range of automatic cannon and anti-tank rifles (there was also a much more famous "Long Solothurn" 20x138B cartridge). This was a belted case, but the rim and case diameters (both 25mm) were virtually identical to the later MG 151 and Hispano rounds.
Incidentally, the MG 151/20 was created simply by adapting the 15mm case to take the shells already in production for the MG-FF (20x80RB). The MG-FF was a modified version of the Oerlikon FF (20x72RB) which was in turn derived directly from the WW1 Becker (20x70RB). The case was stretched to 100mm to make the higher-velocity SEMAG L (later developed to the Oerlikon FFL), but when Oerlikon wanted more power still, they increased the case diameter to make the Oerlikon Type S/FFS. Hispano made this under licence, but then produced a more powerful weapon, the HS 404, which basically took the FFS as a starting point for development. A picture of the Oerlikon family of ammunition is HERE.
Also incidentally, the USSR had earlier followed the same route as Mauser. The first model of the ShVAK aircraft cannon was chambered for a rimmed, 12.7x99R cartridge. This was not much of a performer, so the case was necked up to 20mm caliber to make their standard WW2 aircraft cannon.
Group 5: Based on the US .60" T17.
The second group of four in this PHOTO: .60" T17 (15.2x114), .50/60 (12.7x114), 20mm M39/61 (20x102), 20mm Mk 11/12 (20x110 USN)
In 1939 the US Army issued a requirement for an anti-tank rifle capable of penetrating 1¼" (32mm) of armour at 500 yards (460m). This produced the massive .60" cartridge. The rifle never saw service, neither did the T17 aircraft machine gun (developed from captured Luftwaffe MG151) which was intended to use it. Different designs of .60" machine guns (including revolver and rotary versions) were experimented with but without success.
In the constant USAAF search for higher velocity the cartridge was also necked down to .50", generating up to 4,400 fps (1,340 m/s) with lightweight incendiary bullets. None of the HMGs came to anything and the cartridges are merely collectors' items.
Ironically the Americans learned the same lesson as the Germans had with the MG151 and necked up the case to form the 20mm M39 round which has been the standard USAF cannon cartridge since the 1950s. Its most famous application is in the six-barrelled rotary M61 Vulcan cannon, which also serves as the business end of the Phalanx anti-missile system.
The USN decided that the 20x102 wasn't powerful enough, and their Mk 12 cannon (based on the Hispano) could take a longer cartridge, so they simply stretched the case to 110mm and fitted a slightly heavier projectile. This cartridge was only ever used in the Mk 12 gun (which saw considerable use in the 1950s and 1960s) plus that strange Mk 11 double-barrelled revolver used in the Mk 4 gunpod.
Group 6: Based on the Swiss 20mm FM-K.
The next pair in this PHOTO: 20mm FM-K 38 drill round (20x139), 20mm HS 820/Oerlikon KAD (20x139)
A really obscure one, this. Before WW2 the Swiss developed a range of weapons using a short-recoil mechanism based on the old Maxim design, in unusual calibers like 24mm and 34mm. They also produced a powerful 20mm version which was used as an AA gun (as the Flab.Kan.38) and (to a more limited extent) in aircraft as the FM-K 38. After the war, the 20x139 case was modified by changing the material from brass to steel and fitting a thicker rim, all in the interests of surviving the battering it would get in much faster-firing guns. It achieved commercial success in the Hispano-Suiza HS 820 cannon (later renamed Oerlikon KAD when the companies merged - also used by the US Army as the M139) and the ammunition is also used in the Rheinmetall Rh202, Vektor G1-2 and GIAT 20M693.
Group 7: Based on the 20mm Madsen
The final pair in this PHOTO: 20mm and 23mm Madsen (20x120 and 23x106)
The 20mm Madsen was a popular weapon interwar, being one of the first of the modern, high-performance 20mm automatic weapons, and it saw service in many countries. It was offered in AA, anti-tank and aircraft versions but only the AA model seemed to be a commercial success. The 23mm version of the gun was identical except for the calibre; the cartridge case was shortened as well as necked-out to keep the overall length the same. The 23mm seemed to be aimed solely at the aircraft gun market, and the bigger calibre was selected to increase the projectile size (it held twice as much HE as the 20mm) at some cost in muzzle velocity. The 23mm was proposed for - and tested in - many different aircraft but does not appear to have seen service.
Group 8: Based on the 25mm KBA.
The first pair in this PHOTO: 25mm Oerlikon KBA (25x137), 25mm Oerlikon KBB (25x184).
The development of the Oerlikon 25mm KBA cannon is a story in itself, starting with a US military project in the 1960s, being taken up on its cancellation by Oerlikon and eventually reimported into US service. The cartridge has been adopted as a NATO standard and now has a variety of guns chambered for it; gas operated (Oerlikon), chain driven (Bushmaster and GIAT 25M811) and rotary (GAU-12U). There was even a revolver - the Aden 25 - and a twin-barrelled gun - the GE 225 - but both are now history.
Not satisfied with this, Oerlikon stretched the case to produce the high-velocity 25x184 KBB round, which is also achieving some sales success in AA mountings (land and naval) and light AFVs; rather surprisingly in view of the fact that the gun weighs much the same as the significantly more powerful 30mm Oerlikon KCB.
Group 9: Based on the 25mm Hotchkiss AT round.
The second pair in the PHOTO: 25mm Hotchkiss (25x194R), German 28/20 PzB 41 (28/20x187R).
The rimmed 25mm Hotchkiss case was used in the light anti-tank and AFV gun in French service in the late 1930s. This was taken as the basis for the taper-bore experiments (conducted in 1940 by the Danish Larsen company for the French Army), which were then followed up by the Germans to create the PzB 41, the most significant of the Gerlich type taper-bore AT guns. Muzzle velocity of the PzB was in the region of 4,600 fps (1,400 m/s). It worked well, but suffered from a shortage of the tungsten needed in the projectile.
Group 10: Based on the 25mm Hotchkiss AA round.
The third group in the PHOTO: 25mm Hotchkiss AA (25x163), 30mm Hispano HS 831/Oerlikon KCB (30x170), 30mm Rarden APDS (30x170)
During the 1930s Hotchkiss developed a 25mm AA gun which was adopted by both France and Japan, although it disappeared into history after the war. During the war, the British Manufacturing and Research Company (a Hispano-Suiza subsidiary) produced an unsuccessful 30mm aircraft gun using a cartridge based on the Hotchkiss case. After the war, Hispano developed this idea for the 30mm HS 831, renamed the Oerlikon KCB on the merger of the two companies, which has been widely used as a naval AA gun. It now uses a steel case to withstand the battering of the high-rate gun.
The British Army was looking for a cartridge case of about that power for its new light AFV gun, which emerged as the Rarden. The case reverted to brass to provide better gas sealing, with the aim of preventing gas from seeping back into the turret. The cartridges are now not interchangeable in use, even though the dimensions are the same.
Group 11: Based on the Oerlikon KCA.
The final pair on this PHOTO: Oerlikon KCA (30x173), GAU-8/A, Bushmaster II and Mauser MK30 (30x173)
Oerlikon developed the powerful 30x173 cartridge for its KCA revolver cannon, adopted for versions of the SAAB Viggen fighter. It holds the distinction of being the most powerful gun currently fitted to a fighter.
The USA decided to adopt the case for the GAU-8/A rotary cannon, only the material was changed to light alloy and the priming from electric to percussion. The same cartridge is fired by the Mauser MK30F AA and AFV gun, and the Bushmaster II Chain Gun.
Group 12: Based on the 30mm MK 213.
The first six on this PHOTO are: 30mm Aden LV (30x86B), 30mm DEFA 540 (30x97B), 30mm Aden/GIAT 550/Bushmaster M230/GIAT 30M781 (30x113B), 30mm T328 (30x126B), 25mm Swiss experimental (25x116B), 30mm WECOM (30x100B).
Sadly no photo of the MK 213 round, but it was a 30x85B almost identical to the Aden LV shown here. Not too surprising really, as the Aden was just a copy of the Mauser MK 213.
The French went for a slightly longer case for the DEFA 540 series (also MK 213 copies) before both settled on a case of around 111-113mm (although for other reasons, the ammunition is not interchangeable). It is now used in the M230 Chain Gun carried by the AH-64 (although with alloy cases) and the GIAT 30M781, also a power-driven helicopter gun, and was used in the failed ASP army weapon.
The USA toyed with this cartridge for some years in the 1950s, producing variations on the case within the same overall cartridge length, the best-known being the T328 shown here.
The provenance of the Swiss 25mm experimental is unknown, but it was based on the same case. Incidentally, the British also briefly played with a 20mm cartridge for the Aden in the 1950s. This used the same belted case as the 30mm, unlike the original Mauser MG 213C, which had a rimless 20x135 case.
The WECOM was developed by the US Army Weapons Command for a new helicopter gun, the XM140. This was intended to arm the unsuccessful AH-56 Cheyenne attack helicopter. Later, they had a rethink and adopted the Aden/DEFA case for the M230. Despite the apparent similarity with the Aden/DEFA family, the WECOM cartridge was in fact fractionally diferent in all dimensions.
Group 13: Assorted similarities.
The last three on this PHOTO: 23mm ZU (23x152B), Mauser BK 27 (27x145B), GIAT 30M791 (30x150B)
Three interesting cartridges. There is no claim of a direct relationship between them, but they are so similar in case design that it makes one wonder…during the Second World War the Soviet Air Force used the II 2 Shturmovik ground attack plane armed with the formidable 23mm VYa cannon. Postwar, this was developed (with a change from brass to steel case and minor dimensional alterations) for the ZU AA gun, four of which are used in the ZSU Shilka self-propelled AA system.
The 27mm Mauser BK 27 revolver cannon was designed specifically for the Panavia Tornado strike fighter, although it is also used in Germany's version of the Alpha Jet, in the SAAB Gripen, and has been chosen for the Eurofighter Typhoon and the JSF. A four-barrel naval CIWS mount was developed but not used; a simpler remote-control single-barrel mounting is achieving more success.
The latest round is the 30x150B used in the GIAT 30M791, which has been selected for the new Dassault Rafale. Capable of 2,500 rpm, it holds the record as the joint fastest-firing revolver cannon. The rim, belt and head dimensions are different from those of the original 30x113B DEFA case.
Group 14 (The Old Ones): Based on the 37mm Hotchkiss one pounder.
The first pair in this PHOTO: 37mm Hotchkiss/Maxim (37x94R), Vickers 1 Pdr Mk III (37x69R).
The Hotchkiss round is the daddy of them all in terms of automatic cannon development. Following the Declaration of St Petersburg of 1868, which banned explosive shells weighing less than 400g, it was calculated that 37mm was about the right caliber for a weapon firing shells at least this big. Hotchkiss first developed a 40mm six-barrel rotary gun (based on the Gatling but using a refined mechanism), but rapidly switched to a five-barrel 37mm and achieved huge commercial success. It was the first fast-firing shell gun in the world. Larger weapons in 47mm and 53mm followed, but they never matched the 37mm in popularity. So it was natural for Maxim, when he decided to scale up his machine gun to make a shell-firing "pom-pom", to choose the same 37x94R ammo. It was also used in a variety of small manually-loaded guns, including the ones fitted to the French FT light tanks. It was STILL used in some small French tanks in 1940, albeit with a better loading with a hard-core projectile with a much higher velocity.
Before and during WW1, various attempts were made to fit shell guns to aircraft. The French in particular liked doing this, but the 37mm weapons they fitted were all manually-loaded. The British concentrated more on developing automatic weapons, but found the usual 1 Pdr Maxim (made under licence by Vickers) to be too heavy, so they produced the 1 Pdr Mk III, a much lighter weapon using a shortened 37x69R cartridge. The example shown is an HE round fitted with the super-sensitive No. 131 fuze, intended to detonate on airship fabric.
Group 15: Based on the USN "Heavy One Pounder".
The second pair on this PHOTO: USN Heavy One Pounder (37x136R), USAAF M4 aircraft gun (37x145R)
The "Heavy One Pounder" was the USN's equivalent of the RN's 1½ Pdr described below; an effort to produce a more powerful cartridge for the Maxim light cannon. The weapon rapidly disappeared into history, but the cartridge re-emerged as the basis for a new round (a bit longer and more powerful) developed by Browning for one of his own cannon designs. This was developed by Oldsmobile as the T9 and adopted by the USAAF as the M4. It was mainly used in P-39 Airacobra.
Group 16: Based on the Vickers 1½ Pdr.
The last four cartridges in the PHOTO: Vickers 1½ Pdr (37x123R), Vicker-Crayford 1.59" (40x79R), Vickers 2 Pdr HV naval AA (40x158R), Vickers Class S aircraft anti-tank gun (40x158R).
The Vickers 1½ Pdr was developed for the RN to give more range and hitting power than the 1 Pdr Vickers-Maxim. However, it saw very little use, being rapidly superseded during WW1 by the 2 Pdr, which was the same case necked out to take the larger cartridge. The 2 Pdr saw much service in WW2 as a naval AA gun, and remained in the fleet until the mid-1950s.
Also in WW1, Vickers' Crayford Works produced a light, manually-loaded weapon intended for use as a portable "trench gun" (the kind of role which the 40mm grenade launcher fulfils today) and also as an aircraft weapon. This was known as the 1.59" after the 40mm caliber - in fact the case was just a cut-down 2 Pdr. Although usefully light, the gun was too slow-firing to be a success. Its main claim to fame rests in confusing generations of aviation writers with its nickname of "rocket gun" - a misnomer which was due to an early misunderstanding of its nature.
Just before WW2, the RAF became interested in a large-calibre gun for defending bombers. They calculated that a two-pound shell would be able to destroy any contemporary fighter with one hit, and specified a 40mm weapon capable of being fitted into a turret and aimed with the aid of director control. Vickers duly built the Class S gun based on the old 37mm COW gun but chambered for the 40x158R naval round. A turret was also built and fitted to a much-modified Wellington bomber, but the experiment was considered unsuccessful (a conclusion doubtless influenced by the effect of the muzzle blast in stripping the fabric from the Wimpey's structure). Shortly afterwards, the RAF began to realise that it might be helpful to have some means of destroying enemy tanks from the air (this time their minds were probably concentrated by the sight of massed ranks of Panzers waiting to invade across the Channel) and after various experiments (and some competition from Rolls-Royce) the Vickers S gun ended up being fitted to the Hurricane IID and IV, in which role it enjoyed modest success. The AP loadings were specially developed for the gun.
Group 17: Based on the GAU-8/A case.
The first pair of cartridges in this PHOTO: GAU-8/A (30x173), unknown experimental (35x173).
I couldn't resist including this one. Somebody took the GAU-8/A's case and necked it out to take the shell from the 35mm Oerlikon. I have no idea who, or why, or for what kind of weapon, but I would guess for an aircraft gun, possibly American. If anybody knows more than this, please tell me! The cartridge should be quite a useful performer; I estimate a muzzle energy of 230-240,000 joules, enough to propel the standard 550g shell at 915-935 m/s. And of course, it could fire the AHEAD shells (at a somewhat lower velocity) assuming the FCS problems could be solved.
Group 18: Based on the 35mm Oerlikon KD case.
The last pair of cartridges in the PHOTO: Oerlikon KD series (35x228), Rheinmetall RH 503 case (50x330)
A well-known pair this; the Rheinmetall Rh 503 is an externally-powered weapon available with two barrels; one to take the standard 35x228 ammo, the other to take a 50x330 Supershot round. The reason for the 50mm is to provide the biggest possible "piston area" for firing saboted rounds, particularly the APFSDS. It was intended for the next generation of German AFVs (starting with the 35mm caliber, with the 50mm available as a later upgrade if required) but the end of the Cold War seems to have put a stop to it. The overall length of the two cartridges is the same; only a small part of the sabot protrudes above the neck of the 50mm case. Since then Boeing (or whoever it is this month) has developed a version of the Chain Gun family - the Bushmaster III - to use the same ammunition.
Incidentally, Boeing has also developed a "Super Forty" version of the 30x173 cartridge with the same aim in mind, as a potential upgrade to the Bushmaster II, but I haven't been able to get hold of one of those cases yet…
Group 19: Based (or not) on the 13mm Mauser M1918 case
The cartridges in this PHOTO are the .50 Browning (12.7x99), the 13mm M1918 ATR (13x92SR), a replica of the German AT experimental (13x94), the PzB (7.92x94) and the US .30.50 test round (7.62x99)
The German army introduced in 1918 the first anti-tank rifle; a conventional Mauser bolt-action rifle scaled-up to take a new 13x92SR cartridge. This was also intended for the Maxim-type TuF (Tank und Flieger) machine gun, intended for use against tanks and aircraft as the name implies, but this did not have time to get into action. Also in 1918, the US Army requested the development of a high-velocity large calibre machine gun, primarily for aircraft use, which eventually resulted in the famous .50" Cal Browning machine gun. It is often stated that the .50 cartridge was copied from the Mauser, but a glance at the photo will show that this was (literally!) not the case. The actual sequence of events is more complex. Winchester were given the contract to develop a new cartridge and by October 1918 had produced a rimless 12.7mm design, somewhat slimmer and longer than the current 12.7x99. The project was then handed over to Frankford Arsenal, who in 1919 proposed a new semi-rimmed and tapered case design based on the Mauser round. This was rejected, and Frankford were told to develop a fully rimless cartridge, which they duly did by scaling up the .30-06 rifle round to form the M1919 cartridge. Detailed development of the cartridge and its loadings continued for some years, and only in 1924 was the M1923 cartridge officially adopted.
In the 1930s the Germans commenced development of a new anti-tank rifle and cartridge. The starting point was the 13x92SR, the end point the 7.92x94, also known as the Panzerbüchsen or Patrone 318. However, another cartridge was produced; the 13x94, which used a rimless version of the 13x92SR case. This may seem to have been an intermediate development, but it is also suggested that this was deliberately produced to deceive other nations as to the nature of the new 7.92mm ATR, or possibly to help with weapon development. Incidentally, there was also an experimental 7.92mm cartridge made simply by necking down the 13x92SR case.
The final cartridge in the group is the .30.50 high-velocity test cartridge (7.62x99), included as a comparison with the 7.92x94.
Conclusion
If there is any moral to the above examples, it is that in the military context "necking out" a cartridge to a larger calibre seems to be generally more successful than "necking down". When it comes to hitting power, there is no substitute for calibre!
SOURCES
1. The Machine Gun (Lt-Col Chinn)
2. Jane's Directory of Military Small Arms Ammunition (Ian Hogg)
3. Jane's Armoured Fighting Vehicle Systems
The assistance of the staff of the Ministry of Defence Pattern Room is gratefully acknowledged, also the loan of John Carlin's Vickers 1½ Pdr round.
