Re: Building an Ar-15 , how do I check headspace?
The safest way to check headspace is with the go/no-go gauges. Your face is right next to the port, and if you are off, your can permanently damage yourself, including losing your eyesight in at least your strong-side eye.
Do your health a favor and at least borrow a set of gauges. It is worth it for the end result.