In rimfires, it's not unheard of for the extractor to set off the primer while chambering.
Any instance where it 'hit' the rim due to being fouled either under the extractor or at the breech face, a jammed ext spring (holding it down) could be enough to set off the primer.
I had the money till they made me pay
Then I had the sense to be on my way
I had to stay in the underground
I was in the house when the house burned down.