Quick question on k cups. I was shopping for form 1 parts for my 9mm PCC and keep running across info that 9mm's do better with K cups. Though, I'm not sure how they work. How do they equalize pressure like clipped cones do?

The flat face usually has a scallop in the entry hole to contribute to the turbulence. Then there is also a port in the waist of the K Baffle that vents to the V shaped space on the outside

Yea I've noticed some k baffles having holes in their skirts.. But then do you still need clips now? And if they're clipped and have skirt vents, are they letting too much gas through now?

Yes you need both and they are 180 from each other. The clip or "scoop" helps create some turbulence that encourages the gasses to flow into the vent hole.

Older K baffles had a "mouse hole" at the large end of the V part of the baffle. This was discovered to be unnecessary and newer designs do not have them.

The AAC TiRant and the Dead Air Ghost are excellent examples of hi-performing K Baffle designs.

When I hear the term K cup I imagine some bar maid with huge tracks of land !

Mouse holes were abandoned for pistol caliber but they are still applicable for rifle calibers.You should investigate the so called Dater Hole for your 9mm build.These will lessen FRP and lower overall SPL along with uber small blast chambers.Don't short yourself on baffles used...a count of 9 is good for F1 builds.You are not using AAC baffles with the unique geometry they developed so a few extra helps.
-CL