Ensuring that the chamber is clean insert the headspace gage into the chamber. Insert a fully assembled BCG and charging handle into the upper receiver and using light finger pressure (8.5- 8.75 lbs.) attempt to close the BCG on the gage. Bolt should not rotate into the locked position. The next 3 pictures illustrate this in sequence.

Attachment 5565

Attachment 5566

Attachment 5567

The next procedure is the checking of the firing pin hole on the bolt face. Utilizing the gage you will attempt to penetrate the hole just as you do with the taper plug gage (hammer and trigger pins). If the gage penetrates at any position then the bolt is to be replaced.

Attachment 5568