I don't know if it was intentional on the part of Ruger (or if all RAR models are like this), but the fit between the fat bolt body and receiver near the vent directed towards the magazine is very TIGHT. I put sharpie on the bolt, cycled the bolt a few times, and the shiny areas can been seen in the pics below.

It appears that the bolt-to-receiver fit provides a seal from rearward gas flow. The path of least resistance appears to be the vent directed towards the magazine, but it seems that anything can happen when things go wrong...

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