I have vacuum pumps, if I decide to test a case for leakage, sealing at the primer or neck of the case I can place loaded ammo in a jar full of water and place a vacuum on it. Bubbles escaping from around the primer and or neck of the case will indicate I do not have primers that did not seal and bullet that did not seal in the neck, and if I have a split neck the split neck will show bubbles.
I want all the bullet hold I can get, loose necks cause bubbles.
F. Guffey