Cant find a way to reproduce. I am going to try to test the issue once again tomorrow.

I've logged in to the server for the first time today and checked my barrels.

In a Blue Oil Barrel I have got 3x 30rnd MP5 mag but one with 28 bullets inside.

At the first check all 3 mags were full (3x30 rounds).

I've thought that it may be a bug which allow to replicate ammo.

Nope. After taking a mag into Inventory the ammo count changed to a proper value.

I've decided to log off and check again.

After another log in the ammo count was OK.

I've tested the game client then and logged off and turned off the game so I could once again run it and log in. After 3rd logging in the amount of ammo was OK.

The 28 ammo mag was placed inside a barrel yesterday.
Today (10-15 minutes ago) I've logged in for the first time and only once there was 30 instead of 28.

Haven't tested the issue on different mags yet. It just happened once and will need to be investigated some more which will be done.