The MK258 sabot shell is being buffed this update and the round has a mass of 230gm or 0.23 kg from the manufacturer.

https://www.gd-ots.com/wp-content/uploads/2020/01/30x173mm-Ammunition-Suite.pdf -souce

gaijin buff from dev
For ppl who dont want to convert over, it should be 0.23kg not 0.17
Would need to prove that this does not include the sabot petals as for other rounds gaijin has considered the statement “Projectile Mass” to include the sabot petals.
Would be a very nice buff though as it should increase pen by quite a bit.
PMC 287 is also 0.235g but they model it as 0.17g so idk.
Cartridge mass usually means the overall weight of the entire round, which would include both the projectile and the case, but also the propellant and primer. So cartridge mass doesn’t mean much in this case.