1. let the bolt and carriers snap fwd on an empty chamber
2. set weapon to fire
3. pull trigger
4. measure gap between bolt head and bolt carrier Should be .004-.020
5. change rollers to obtain correct gap

Caution...some rifles built on parts kits have a ground head to give a false gap. If the head has been ground in any way replace the head and readjust the bolt gap to .004-.020