Everything I've read has uniformly stated that when rust bluing a set of barrels, a vent hole in the bottom rib is essential because during the repetitive boiling process, the air trapped between the top and bottom ribs expands when heated to 212 degrees and the resulting pressure can pop a rib loose. But I've also noted that original condition Parkers don't have a vent hole like most other brands of vintage doubles, and wondered how Parker managed to rust blue its barrels, which presumably had to be done after both the top and bottom ribs were soldered in place.
Is it simply not true that a vent hole in the bottom rib is necessary for rebluing Parker barrels? Has anyone here ever tried to rust blue a set of Parker barrels without a vent hole and had the rib pop loose during the boiling process?
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