Light AFV guns and the WCSP and FRES Scout projects

The cannon mounted in the turrets of LAFVs (Light Armoured Fighting Vehicles) have two principal uses: one is to engage their equivalents, for which they need guns powerful enough to penetrate their armour when using AP ammunition, while the other is to engage softer targets; unarmoured vehicles, buildings and other cover, and troops. 

A gun-armour race has been slowly developing among LAFVs. The previously common 20mm calibre, particularly the 20x139 used in the Rheinmetall Rh 202 among others, has mainly been superseded for this purpose by the 25x137 NATO round, principally in the ATK M242 Bushmaster Chain Gun, but the 30mm calibre is now standard for almost all new developments. The British 30mm Rarden L21A2 gun (30x170) has of course been in service for decades, as have the Russian BMP 30mm guns (30x165), and these have more recently been joined in service by the Mauser MK 30 and the ATK Bushmaster II (since replaced in production by the marinised MK44 version developed for the USMC's EFV), both in 30x173 calibre. One oddity is the 1950s Soviet 30x210B cartridge, developed for the NN-30 naval gun, which was adopted by Yugoslavia in the 1980s for the Zastava M86 (single ammo feed) and M89 (double feed) AFV guns; this has been revived for new Serbian LAFV developments.

Moving up in power, the 35x228 Oerlikon round as used in the Oerlikon KDE has been in service for some years in the Japanese Type 89 MICV. The Netherlands and Denmark have also chosen this round for their new CV9035 MICV, only this time in ATK's Bushmaster III. The 40x365R Bofors L70 has been in Swedish service for some years in the CV9040, and the round is also used by the new Korean Infantry Fighting Vehicle. In the late 1970s, Germany considered the idea of a Marder MICV armed with a version of the Bofors 57mm in 57x438R calibre, but this went nowhere.   

A few years later Otobreda of Italy and IMI of Israel co-developed the self-loading 60mm HVMS 60 (High-Velocity Medium-Support) around new 60x410R ammunition. After a while, the two firms parted company and continued separate developments of the gun and ammunition. The only sale achieved so far is by IMI to Chile, to rearm some old tanks (apparently with a manually-loaded version of the gun). 

he largest conventional cannon currently being promoted is the new Russian AU-220 turret containing a version of the old 57mm S-60 AA gun in 57x347SR calibre. This is initially intended for rearming the PT-76 light amphibious tank but is said to be suitable for other LAFVs.