Chris Bartocci made 3 parts video covering Bolt Carrier Groups
Part 1: ARs
Part 2: AR10 bolts
Part 3:Bolt carrier finishes
Small Arms Solutions is back on Youtube
https://www.youtube.com/channel/UCn_AGhwovzeWrnqHFJpYWaw
However, the previous videos were lost, so it seems like Chris is uploading those videos again.
From: Small Arms Solution