Update 7/12/2021 : Added "TF2-" prefix to the name for better searching.

So yeah, the Sentry Gamma made by ChoEv, derrived from their old design of Xturret Sentries X, now available for Gmod.

You can find the original SFM addon here:
https://steamcommunity.com/sharedfiles/filedetails/?id=2297858575

Includes:
choev\sentry_gamma\sentry_lv3.mdl

Credits:
ChoEv - Model and Textures.
NeoLin - Porting to Garry's Mod.