A delayed fire is a called a hangfire. For some reason, the powder may not be receivingthe full charge/proper chargefrom the primer for proper powder ignition(could be one or more of the variables you mentioned regarding the primer, primer pocket, etc.), the powder itself could not be working correctly, or a combination of the two. I WOULD NOT FIRE ANY MORE OF THESE! Use an inertia tool to unseat the bullet on a round that did not go off. I would not do this unlessit has been at leasta couple hours sinceyou tried to fire the round. Inspect the primer while it is still in the case to see if it ignited. Also inspect the powder. I strongly suggest doing this with a well experienced and safereloader.

If a round does not go off using modern smokeless powder, wait at least one to two minutes with the firearm properlyheld and pointed in a safe direction before you unchamber the round. Some say this should be at least 5 minutes with black powder.