An introduction to collecting 23-28mm cartridges

© Anthony G Williams

A version of this was formerly published in the July and August 2007 issues of The Cartridge Researcher, the bulletin of the European Cartridge Research Association

This class of ammunition has never been as popular as the 20mm rounds (see separate article). Perhaps a dozen rounds in this class can be considered really successful, in terms of being widely used. Several others were fully developed but saw little or no use. As before, this article will be concentrating on those which saw actual use - even if not much!

Group 1: up to 1918

The first cartridge shown is the rare 1 inch Gatling round (25x88R), in this case a replica of the French model made with a coiled brass rather than drawn brass case. US models come with drawn brass cases of different lengths (one slightly longer, one much shorter). This was the largest of the original Gatling series of rounds, and saw little use. 

Far more common is the 1 inch Nordenfelt (25x94R), which entered British naval service in 1881 in a manually-cranked, multi-barrel close-defence gun. This typically had a steel-cored bullet as shown, but lead bullet loadings were also known.

This is easily confused with the third round, the 1 inch Aiming Tube, used for sub-calibre training.  This used the same case as the Nordenfelt, but a lead bullet of a different shape, and was also often used with electric priming.

Next come two rounds designed for automatic weapons: the Vickers 1 inch (25x87R) and the 25mm Revelli-FIAT (25x87). The Vickers was designed for an aircraft gun in 1914 but this saw no British service, being only made in Italy by Vickers-Terni. This saw limited service in some Italian aircraft (one picture shows one installed in a Caproni Ca.3 bomber) and was purchased by the Swedish navy in 1922 for arming some submarines; the only known official adoption. The Revelli-FIAT was inspired by the Vickers-Terni, but perhaps too closely as production was curtailed when Vickers threatened legal action over patent violations. The cartridge case was modified to a more modern, sharp-shouldered, rimless type, but the gun was magazine-fed (the Vickers was belt-fed). The gun was installed in a variety of Italian aircraft and was used in action in WW1, but was not popular due to the tendency of the HE shells to explode prematurely. Both the Vickers and Revelli-FIAT cartridges are uncommon.

1 inch French Gatling (replica), 1" Nordenfelt, 1" Aiming Tube (note fired projectile), 1" Vickers, 25mm Revelli-FIAT

Group 2: 1918-45

This period saw a marked increase in the size and performance of the cartridges in this class. The first to be developed was the 23mm Madsen, which used a 23x106 cartridge formed by necking-out and shortening the case of the popular 20x120 Madsen round; the guns were identical, except for the barrel. The idea was to trade velocity for high-explosive content to increase the effectiveness of the gun in its aircraft applications; the HE shell contained double the HE of the 20mm. The 23mm Madsen featured in various experimental installations, but probably never made it into service except reportedly in Argentina and – just possibly – in a couple of Hawk 75 planes bought by China. The cartridge is very rare.

The next development was the 25mm Bofors, which was introduced in 1932. The initial m/32 model fired a 25x205R round, but a later m/38 version fired a modified 25x187R. The gun seems to have seen little use except for its purchase by the USSR, which modified the case yet again (to a slightly longer but slimmer 25x218R) and put it into service during WW2 as the M40 naval AA gun. Regrettably I have no examples of any of these in my collection, so they do not feature in the photograph.

Next came the 25.4mm Vickers, which used a 25x189 cartridge. This is described and illustrated in a separate article on this site so no more will be said here, except that it only appears to have been used in the Vickers-built Argentinian training cruiser La Argentina. It is exceptionally rare.

The next development came from France, in the form of the 25mm Hotchkiss. Two very different cartridges with this designation were made simultaneously: the 25x163 for the Mle 1938 automatic AA gun (adopted by the Japanese Navy as the 25mm Type 96) and the 25x194R for the Mle 1934 manually- loaded anti-tank/light tank gun. The AP loadings for these rounds are unusual in that they use a jacketed projectile, just like a big AP rifle bullet. Both of these cartridges are fairly common.

The same case was indirectly used as the basis for the German 28/20 Gerlich squeezebore round (28x187R) used in the PzB.41 anti-tank gun. Original examples are rare: the magnesium projectile tip tended to corrode so most encountered now (like the one in the photograph) have a replica tip.

Attention now switches to the USA and the 1.1 inch naval AA gun, made only in a four-barrel mounting. The big 28x199SR cartridge was powerful, but the gun was slow-firing and required careful maintenance, so the 40mm Bofors was preferred. The one in the photo has a replica projectile.

The US also produced several automatic guns in the .90 inch series (designated T1-T4) of which the 23x139SR for the T4 is by far the most common, but these remained experimental. 

Another cartridge which was never formally adopted for service was the 23x122 for the French Hispano-Suiza HS 406 and 407 aircraft cannon, a big brother to the famous 20mm Hispano HS 404. This was very powerful, but was still being perfected in 1940. One fighter plane probably armed with this gun took off for an anti-tank mission during the Battle of France, but was shot down.

The USSR now comes into the picture with the powerful 23mm VYa (Volkov-Yartsev, the designers) aircraft cannon. The 23x152B cartridge had a brass case, unlike the postwar AA variant, and is much less common. Brass cases with postwar dates were used for subcalibre training.

Finally is the Swiss 24mm Tb41. The 24x139 cartridge was used in two related self-loading guns, one a light anti-tank gun, the other for arming light AFVs.

23mm Madsen, 25mm Hotchkiss AA and AT, 28/20 Gerlich, 1.1" USN, 23mm HS, 23mm VYa, 24mm Tb41

Group 3: 1945+

For several decades after WW2, the Soviet Union monopolised new service developments in this calibre range.

First was the 23x115 cartridge introduced in the NS-23 aircraft gun which emerged at the end of the war. It was soon replaced by the faster-firing NR-23, then the even faster AM-23, before the famous twin-barrel GSh-23 made its appearance in the late 1950s. In the 1970s, the cartridge was retained for the GSh-6-23 six-barrel rotary gun. All of these were designed as aircraft weapons. The ammunition is common.

Next comes the 25x218 naval AA gun cartridge, a rimless version of the 25x218R M40. The ammunition is a lot more common than it used to be.

The 23mm ZU AA gun used basically the same 23x152B case as the VYa, but made of steel, with a different primer and different loadings so it is not interchangeable. It is now very easy to find.

One oddity is the 23x260 for the Soviet Rikhter R-23 reverse-loading aircraft revolver cannon of the early 1960s. The cartridge looks like a length of plumbing pipe, with the projectiles concealed within it and a tapering base without a rim or extractor groove. It did see operational service in some Tu-22 bombers, but the ammunition is exceptionally rare and is not shown here.

Attention now switches to the west. The USA attempted to develop a very advanced 25mm aircraft gun, the GAU-7/A rotary, in the late 1960s. This had a combustible case and used a telescoped layout, with the projectile buried within the case, but technical problems defeated the project.

The most successful of all of the 25mm rounds, the 25x137 Oerlikon, was a much more conventional effort, with a steel case. This is a standard NATO round, used in a variety of guns, including the Oerlikon KBA, M240 Bushmaster Chain Gun, GAU-12/U five-barrel rotary, and GIAT 25M811. Ammunition for this is of course more common than for any other in this calibre, with a wide range of different loadings.

The 25x137's big brother is the lengthened 25x184, used in the Oerlikon KBB gun. This has been far less successful (probably only used in a CIWS adopted by the Turkish navy), but is still not too hard for collectors to find.

Finally comes the odd-calibre 27x145B Mauser, designed for the BK27 aircraft revolver cannon which is in widespread European service (including in Tornados, Gripens and Typhoons).  The gun has recently been adopted by the German Navy in the remotely-controlled MLG-27 defensive mounting.

23x115, 23x152B, 25x218, 25x137, 25x184, 27x145B

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