The TOOL, bolt head, rifle as shown by Son will work where it's a very small amount of underturn but not if it's a lot (all apprentices of the era made them.....). We never had a problem because we always had a tray full of bolts/bolt heads to fit/try before finally adjusting up and numbering. But I would turn a gnats knacker off the bolt head shoulder in this case so that you get the MINIMUM of overturn. Bolt head is really tough material and can take it