another Q for arjuna/sharabhanga

[Singhi Kaya]

What is bhairavi chakra? Is it a shakta practice or shaiva?
Is it a group or refers to chakra sadhana in tantra?

Is kalachakra in buddhism related to this?
.

[Arjuna]

Bhairavi-chakra is a group secret upasana of Vamachara, one of chakranushthanas (or Shri-chakras). Usual minimum requirement is 4 men + 5 women. It may involve phisical maithuna or may not (in second case it is still done but in bhAvanA).

Bhairavi-chakra is referred to in Saundarya-lahari (indirectly: caturbhiH shriikaNThaiH shivayuvatibhiH pa~ncabhirapi...) and Mahanirvana-tantra, as well as in many less known and easily available texts.
In Shrividya it is directly related to Kamakala-dhyana.

Being of of the most sacred rituals of Kula, nowadays it is rarely performed — because it requires high adepts (males only purnabhishiktas strictly) join together...

[Arjuna]

Kalachakra as i know is not related to this.

However in Kalachakra (it is a school of Tantric buddism) Vama-marga sadhanas are practiced as well. Sexual rituals are at the heart of sadhana of Kalachakra in the same way as in Kaula-tantrism.