Some of the cases with loose pockets jetted hot gas between the primer cup
and the pocket and started to mark the breech-face.
Even this--the softest pistol primer cup
available--simply does not flatten much in loads at these modest pressures.
Winchester recently added the Ranger "T" series that features a modified SXT bullet, brass primer cup
and is loaded to deliver consistent ballistics regardless of barrel length.
When the firing pin struck the primer cup
, the explosive was crushed between the cup and anvil, and it ignited.
This sort of perforation takes the form of a hole in the primer cup
the size of the firing pin tunnel where the cup material is simply pushed into the firing pin tunnel by the pressure.
This should result in the primer cup
's face lying a few thousands of an inch below flush with the case head.
The Benet-primed cases don't have a "balloon head," since in such cases the primer cup
rises like a prairie dog mound from inside the head of the case (why balloon-head cases have more internal capacity than solid-head cases).
Sometimes the pressure is enough to push the primer cup
and anvil from the primer pocket.
Inasmuch as I wanted to load for a wildcat bottleneck cartridge, the 6 mm BR Remington--which is based on a .308 WCF case--the only change necessary was the large primer cup
to the small primer cup
on the automatic primer feed.
The liquid should wick around the primer annulus (the ring-shaped depression where the case head meets the primer cup
), completely sealing the case without depositing too much sealer.