The CV90 120 is fitted with a RUAG 120mm smoothbote gun. It has a lower recoil than say the Rheinmetall 120mm fitted to the Leopard 2 so it is more suited to smaller tanks. The only tanks in service which use the RUAG gun, as far as I know, are the upgraded M-60s (Pheonix) of the Jordanian army. The Jordanians also have a proposal to equip their Challenger 1 tanks with an unmanned turret called "Falcon" using the same gun. I have seen some reports that the Jordanians have in the interim replaced the British rifled 120mm with the RUAG weapon in the existing turrets of the Challengers.
The RUAG gun was initially developed by the Swiss with replacing the 105mm of the
Pz68 in mind (other 120mm guns didn't fit the relatively small turret without extensive turret modifications), so that it got more firepower and could use the same ammo as the Leo2s the Swiss bought. Trialled but never adopted.
http://www.army-guide.com/eng/product1397.html
http://www.janes.com/extract/jdw99/jdw01877.html
Of course, the concept of equipping an IFV with a large caliber cannon to arrive at a light tank is far from new. Argentinia has developed and adopted a Marder-derivative IFV (VCTP) as well as 105mm gun toting derivative called TAM and a 155mm SPGH derivative (using the turret of Oto Melara's Palmaria). TAM weighs about 30.5 tons. In 1973 the Argentine Ministry of Defense drew up the requirements for this light tank, which entered service in the 1980s.
Then there is the AMX-10P PAC-90 / Marine, with 90mm turret, in service with the Indonesian marines. However, I suppose, the AMX-10P could possibly sport the 105mm turret of the AMX-10RC wheeled reconnaissance vehicle. This turret was also used in the CV-90105, the predecessor to the CV-90120 .
Ascod IFV has been offered with a LIW LMT-105mm turret from South Africa and with the 105/120mm HitFact turret by Oto Melara. MCV-80 Warrior trialled with a Belgian Cockerill CM90 two-man turret (recce version) and also with the Rooikat 105 turret (this light tank was proposed to Malaysia, the Republic of China, and Thailand.)
But the Swedes has obviously taken the idea furthest along. Probably with the same needs in mind that spurred the development of the IKV-91 tank destroyer
