Looking at image search results for this model of CZ it seems that quite a few earlier production units had poor matching between surfaces/edges of the feed ramp and the bevelled edge of the barrel, resulting in flat nosed and hollow point bullets sometimes catching and failing to feed. Seems a lot of users didn't quite have such bad failures, but did see asymmetrical damage on some hollow point rounds when pulling them back out without firing. Some work with Dremel bits seemed to be the most common solution.
My TNW Aero has a less complete feed ramp, being two short bevelled edges cut into the chamber area with a small gap between them. It came to me quite rough, certainly no polishing done, just halfway decent machining and the black residue of the heat treatment process. I did a bunch of rounding over of edges as copper jackets on Remington UMC 147gr (flat tipped FMJ) were showing significant denting when just dropping the bolt and then pulling them to inspect. After thoroughly polishing, nothing sharp anywhere near the entry point, I stopped seeing any damage at all. Haven't tried JHP yet but I'm picking up a bunch tomorrow so then I'll see if the changes work with this more challenging round - Winchester white box 147gr JHP.
With the Aero I've found that buffer spring tension plays a very significant role in clean ejection and feeding. Even a 1 turn change in the stock results in very notable changes of function. I've found the ejection cycle a bit too violent, so tested a heavier bolt by adding a 3oz weight to the bolt handle and turning the buffer spring for 2 full turns less preload. The result was clean ejection and feeding, with less felt recoil and I think less port noise owing to the slightly increased delay before ejection with the added weight. So I ordered a tungsten rod scrap piece from a Chinese shop and when that comes I'll drill out the buffer weight and use some JB Weld to fix it in place, increasing the net weight by 3oz. I'll chop the main spring a little too, as cranking out the stock too much would leave that area barely attached and weak.
I'm doing this stuff because I want to standardize on 147gr for consistency, owing to a lot of stuff I've seen about various blowback operated 9mm carbines being ammo fussy. Using just one bullet weight and power level and fine tuning the gun to cycle those ought to make for trouble-free operation. Seems it's just part of the deal with blowback, same as fine tuning gas operated systems is quite fussy on some models of AR.
