This is because in the "M9K Heavy Weapons" addon the PSG-1 textures are misplaced & misnamed in major ways.
Putting this "Giant's Lair PSG-1 Fix" into "garrysmod/addons" folder may help in the mean time.
https://www.mediafire.com/file/xrb8racxatv1at7/Giant%2527s_Lair_PSG-1_Fix.zip
Restoring the CS:S/HL2 viewmodels to their originals. This can only be applied server-side.
To get the original ironsight values, go to the May 26, 2013 TTT github repository (Before the before the "SWEP Hands" update on Jun 7, 2013)...
A minor addon that adds optional quality of life improvements to TTT.
Includes a new ragdoll system that carries velocity from whichever direction the player was moving. ( server cvar: ttt_newragvel 1 )
It has options to:
Allow double-clicking in the buy menu. ( server cvar...