Do you use Java 8?
Yes

What version of Minecraft do you use?
1.12.2

What version of MinecraftForge do you use?
14.23.5.2854

What version of SanLib do you use?
1.5.1

What version of Turret Mod Rebirth do you use?
4.0.0-beta.3

What is the issue/bug you have encountered? Give us a short description.
Turret upgrades can be duped by shift clicking them into a turret when opened with a TCU.

How can it be reproduced?
Have 2 or more of the same upgrade stacked together
Shift click it into the turret after opening the upgrades via TCU

A good solution would be to just make them nonstackable.