Thanks for posting your experience up Jay; however I'm disappointed to hear that Westjet didn't follow their own policy. All that should have been required was to fill out a "firearms declaration" form and boom you're done. It's not the airline's place to determine what is and what isn't an "acceptable" firearm.
That being said, I've had a similar experience, and like you I found that patience and "keeping it cool" goes along way.
When flying home for summer vacation in 2005, I took my CA AK74 (wood and steel, authentic!) with me to attend a game that emptymags was hosting in Edmonton. On my way back to Ottawa, I filled out my firearms dec at the Edmonton airport, and was told like to you take my guncase (locked) through oversize baggage.
The guncase was scanned, and again I had the "buggered out eyes" reaction, and a lot of talking on the tech's radio. I was asked if I could open the case, and I said sure, did so. Two airport security officers and three airport staff crowded around my case as I explained that it was an airsoft rifle, and like you Jay I showed them the magazine well and removed the dust cover to show them the mechbox.
The baggage tech doing the xray turned out to be from Serbia, and immigrated after the wars in the 90's, he was only too happy when I told him "go nuts" when he asked to hold it. He was shouldering it with a mag slapped in, cocking the fake bolt etc...
Anyway, that's my similar story; again thanks for sharing Jay.