These various factors contributed to decisions not just in France, but also in Germany, the United Kingdom, and the United States, to abandon previously plans to add larger caliber main guns to their respective main battle tank designs. The end of the Cold War and a reduced emphasis on conventional ground operations also played a part in the death of those programs.

A size comparison of Rheinmetall's original 120mm gun, its extended L55 variant, and its earlier, proposed 140mm type. It's new 130mm design is shorter than the 120mm L55.

There has already been a broad level of renewed interest in the potential of larger caliber main guns for tanks across NATO since 2014, when Russia seized of Ukraine’s Crimean Peninsula and subsequent began actively supporting for separatists in that country. After that, the United States and other members of the Alliance rushed to reinvigorate their more traditional combat capabilities, with a particular emphasis on improved armored vehicles, among other things.

It may become increasingly attractive then to go to a larger caliber, but shorter main gun instead, regardless of the design demands and logistical issues this might create in the process. It’s worth noting that Rheinmetall’s experimental 130mm gun is shorter than its improved 120mm gun, but is more capable.

A longer barrel might require higher-pressure ammunition to ensure the shell reaches a consistent peak speed before leaving the muzzle, which would put more strain on the entire gun. The extended proboscis would also increase the tank’s physical footprint, potentially making it more difficult to transport. The U.S. military has had to contend with similar issues in the development of its extended-range 155mm howitzers, which also feature significantly longer barrels than their predecessors.

At present, Nexter and Rheinmetall have yet to publicly unveil their proposed design, even in mockup or model form, with or without a new, larger main gun. Nexter and German armored vehicle maker Krauss-Maffei Wegmann, which merged to form KMW+Nexter Defense Systems (KNDS) in 2015, did debut what they called European Main Battle Tank (EMBT) at the Eurosatory arms fair in 2018, but this vehicle featured a Leopard 2 hull with a standard Leclerc turret with a 120mm gun.

Beyond tanks, various NATO members have been similarly looking to up-gun lighter armored vehicles to either better match or outrange their Russian counterparts, too. The U.S. Army alone has added a 30mm cannon to some of its Stryker wheeled armored vehicles, which previously only had a .50 caliber machine gun or 40mm automatic grenade launcher. That service is also looking to replace its tracked Bradley Fighting Vehicles and its 25mm main gun with a new design that might come armed with a 50mm cannon. 

Rheinmetall

At the same time, these developments may be reaching the limit of how much performance it is possible to get out of a 120mm gun and still have that weapon be practical. Lengthening the barrel is a relatively easy way to increase range and muzzle velocity, but creates new problems the longer it gets.