News is saying he used a B&T Station Six, it doesn't look like he's twisting to operate a Welrod action in the video to me. It looks like he's racking a slide. He doesn't hesitate like he discovers it's jammed after the first shot, he already goes to rack it because the subsonic cartridges he's using won't cycle the action with the (edit:) suppressor on without a Neilsen device.