I know this was posted in 2007 but the pics have disappeared. The PS90 has a bolt catch. You have to pull the charging handle and keep the moving parts assy back and then insert your finger into the ejection well and push the obturator up. The obturator has a spring loaded catch that will catch on the side of the hammer assembly and prevent the bolt assy from moving forward. To release, pull charging handle back and let go. FN once inserted instructions with the PS90's on the operation of this part but no longer does. Also, one can depress and lock this obturator when not in use or when your are in extreme environments to keep foreign materials out of the action. When a range officer declares open bolt condition, this may be good to know.