The bolt head on a #4 should have the bolt fully screwed in and the bottom of the bolt head should be close or touching the front of the bolt body. The amount the bolt head mentioned is the maximum the bolt head should swing past being fully engaged. Never have the threads take the strain when fired. Armor's when fitting bolt heads at the arsenal or factory had bins of bolt heads. if one didn't match up according to the specs then they would simply try another one until the fit was according to specs. Kinda a trial and error thing. Frank