[Starbish]

i tried to figure out how sentry gun rotates when seeking targets but i had no luck.

at first i thought it was animation but it seems not as it's kinda creepy.

Is sentry gun consisted of 2 parts? (one is upper and another is for standing(?))

If so, how can i rotate the upper one only?

Seems like tf2 game itself did something to rotate upper one...

[asherkin]

It uses poseparams / blend sequences.

[404UserNotFound]

Here's some notes I made on m_flPoseParameters that may be helpful to you. Simply switch out the entity being targetted in the examples with the entity of the sentry gun, use HLMV to figure out which poseparams thing does what and go from there.