AR15 bolt notch reason.

[Cane55]

I understand the reason for the AR15 boat tail in order for the gases to expand against the boat tail gas rings to start the BCG moving etc., but never understood why there’s material removed from the other side of the gas rings. Does anyone know? Here’s a photo of exactly the notch I mean. What’s the reason for this? Thanks in advance to anyone who knows.
66279

[lysander]

Reduce the weight of the bolt, and reduce the surface area that could drag on the ID if fouled.