take the bolt head and try soaking it in a carbon remover solvent or some type of cleaner and dig around in the hole with a needle...if you were blowing primers its most likely the ejector pin hole has carbon build up in it. i had the same problem when i blew primers out of the pockets in my 300 win mag,broke the ejector and the back part of it was stuck in the hole.

also i wouldnt shoot anymore of that ammo if i was you...also look closely at the hole in the bolt head and make sure the firing pin hole isnt worn out.