Originally Posted by Tyler Kemp
I think the headspace is set a little long, with the case in the chamber sometimes the firing pin has to push the case into the chamber all the way, then the second time is fine.
And then the third time.
Looks like the only way to get the final sharpening of the shoulder will be to fire with bullets.
If you were to take Cowboys suggestion, Use a bullet to fireform with, seated long to hold everything snug on initial firing, you will end up with a better job the first time around. A pound of unique is about the same price as a used full set of rcbs loading dies. After which you can potentially form 70,000 brass with. Your misfires are coming from the unsupported case slopping around in the chamber, with enough slop sometimes that the firing pin is not long enough to reach. If still insistant on shooting blanks, at least size up a caliber and then partial necksize back down to create a false shoulder to hold your cases back against the bolt.
The words sometimes, and headspace too long can't go in the same sentence. Sometimes, and brass too short, now that works.