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Little precisions to the above;
It was re-assembly and not dis-assembly wich was in cause with the Mk III bolt (you got it right at the end of the sentence). And it,s a "out of timing" of the mating threads of the bolt head and the bolt body wich caused the failure, not really a "upside-down" procedure.
Also, on the mk III, the rear lug (last portion of the screw thread of the bolt head) is hammering on the bolt stop and the first versions used a small diameter of bolt stop, wich was cured in later by using a larger diameter bolt stop. This small diameter was mating on on smal surface and the use of a larger diameter bolt stop provided much more mating surface.
The bolt heads were also re-heat treated in England, under suspect procedures, resulting in soft and brittle heads.
It was re-assembly and not dis-assembly wich was in cause with the Mk III bolt (you got it right at the end of the sentence). And it,s a "out of timing" of the mating threads of the bolt head and the bolt body wich caused the failure, not really a "upside-down" procedure.
Also, on the mk III, the rear lug (last portion of the screw thread of the bolt head) is hammering on the bolt stop and the first versions used a small diameter of bolt stop, wich was cured in later by using a larger diameter bolt stop. This small diameter was mating on on smal surface and the use of a larger diameter bolt stop provided much more mating surface.
The bolt heads were also re-heat treated in England, under suspect procedures, resulting in soft and brittle heads.