/t/ → /k/
Now the plosive alveolar /t/ is followed by a sound that is produced at the back of the mouth, a velar (a /k/or a /g/), so the /t/ is assimilated into a voiceless velar /k/. As you can see, the place of articulation changes, but the manner and the voicing (voiceless) are kept.
Therefore,
/t/ (followed by /k/ or /g/) becomes /k/
Put that gun down. ǀ ðæk ˈgʌn ǀ
And here are some natural ocurring examples:
He greets ticket collectors and stationmasters and they return his salute (Julian Barnes, KUSP).
As ideas emerge, get going, start writing and a form will start becoming aparent to you (Michael Rosen, OpenLearn).
And so, Charles’s problem really was about perception of catholicism at court (Mark Knights, BBC4).