Obviously there was no brazing. Plainly this is a quality control issue and perhaps, a manufacturing process issue. The same sort of thing occasionally happens on Winchester M 70's.
Now, what aspect of the Mossberg design as opposed to that of the Winchester turns this from a maddening inconvenience to a catastrophic accident? Anyone? What old Mauser 98 feature could be easily incorporated in a multi-piece bolt to absolutely prevent an unlocked bolt from firing? GD
I believe the M70 has the cocking cam in the handle AND body, not just the handle. The cocking piece would force an unlocked bolt to rotate closed, then probably not fire due to loss of energy. At the head end, the Mossberg bolt head is pinned to the body. Most others are one piece, silver soldered, or brazed to the bolt body.
The Mauser has a ridge on the firing pin the fits into a valley at the rear of the bolt head when fired with bolt locked. If not locked, the ridge missing the valley prevents the firing pin from going fully forward and hitting the primer.
Bruce
Mauser firing pin
