I've had this twice. Once I fired a second round, long story, learnt my lesson, no damage to gun (CZ).
The first round I drove out forward, I think a cleaning rod is too bendy and baught a steel rod from B&Q for the job. All I needed to do was tap it with the end of a screwdriver, I was surprised how easy it was.
2nd round was not even properly in the barrel, that on I pushed backwards into the chamber.
The rifle still shoots better than I can.
If you don't have a rod, how do yo clean your HMR? That could start a lively discussion!
I like the HMR.