what Udmurtia needs is obsolete shells to put in obsolete guns.
Why write about things, you don't have the slightest idea about?
The most modern American towed howitzer is the M777, having been introduced in the early 2000s. Apart from the addition of digital fire control (which could be employed on predecessors as well, in theory), the entire purpose of the M777 was for it to be lighter than its predecessor - the M198 - which was introduced in the late 1960s.
The M198, in turn, was an intended as a more lightweight replacement for the M114 howitzer. Unlike the M114, the M198 could be dropped by parachute, or hauled by a Chinook or Super Stallion helicopter.
The M114, introduced in 1942, was itself a further development of the Canon de 155 C (modèle 1917 Schneider). It differed from its predecessor, by being able to elevate the gun higher, and having a less cumbersome carriage.
In other words, American guns, just like Russian guns, haven't changed very much since the First World War. The most widely used shell in the M777/M198/M114 is the M107 shell. Designed in the 1930s, as an improvement to a World War I-era French shell.
Who is using old guns, or outdated shells, in other words - is a big question. Not that it matters either. Would you prefer to get killed with a democratic and righteous 155mm shell, or a freedom-hating and primitive 152mm shell?