COD 20 About (Livar 9mm submachine gun) zombie mode gun skin

[简简不是筒筒]

I've tried everything, but I don't know why my kills aren't adding up. I think the battlefield upgrade stated in his conditions is the upgrade of the enhanced machine, but when I guided a large wave of zombies to follow me, and then killed them immediately after the upgrade, there was no progress, and I didn’t even know that I How did the cumulative number of 4 kills come from?