I don't know how it would be headspace though. Headspace on a rimmed case would, to me, suggest that either it is too great, in which case it would consistently not fire (pushing the bolt wouldn't help, since presumably the bolt is in full battery, or it has too small of a headspace, and the bolt wouldn't fully close, in which case it would likely fire fine and on a 22lr you'd possibly never even know it was too small
Curiouser and curiouser to me....
Hey I got a crazy idea.... Check your extractor claw! Is it riding on the slot in the barrel end? Maybe the barrel isn't indexed quite right, causing the extractor claw to draw on its way in, slowing the bolt down? Or maybe the extractor claw leading edge is really rough, or the claw won't pivot smoothly so it gets hung up on the case rim....
That actually sounds a little plausible now that I think it over....