A family member returned from the range yesterday with my Anderson AR10 and reported the following problem: after seating a fresh mag and closing the bolt, he pulled the trigger and had a fail to fire. Cycling the bolt and loading a fresh round successfully ran the remainder of the mag. Each time first round in the mag. Firing my reloads. The cartridges showed a veeeeeery slight dimple, indicating the firing pin contacted the primer but did not set it off. Military brass. Primer is set at proper depth. CCI large rifle primers. He had issues on a total of 3 of 150 rounds during this particular shooting session. When I take down the rifle, what should I be looking for? I'm thinking firing pin and channel, but a slow pin would have affected any round in the mag, not just the first.