Unsure about the origin, but the phrase can get formalized…
While stationed in Panama (w/ the USAF) I worked in Current Operations (planning and scheduling flights ,etc). It was a three week cycle: the first two weeks planning, etc (during which time I could fly - woo-hoo!); the last week was your week “in the barrel”. You were the poor sap on call for any mission that fell apart, and generally the guy who everyone called when they couldn’t make something work.
In fact, whoever was running that week was called the “Barrelmaster”. People from all over Central and South America would call up and ask for the “Barrelmaster”. They didn’t know who it was or what the term meant, but that’s who they wanted to talk to. We figured out that it probably referred to “the guy who’s gonna get screwed all week”, but once again, it probably originated as a joke and ended up as the only way people knew how to refer to a certain job.
FWIW, it WAS a screw job!
