Consider checking under the extractor for a build-up of crud (a weakness of the design -- Most CZ clones open up the back of that channel so that junk goes into the firing pin chamber).
And, of course, consider replacing the extactor spring with a Wolff extra-strength extractor.
The only ammo I've ever had problems with in my CZs was AAA (brand) ammo, which was poorly quality controlled. Some was so bad that it wouldn't even chamber in my Browning Hi-Power (too long!).
Right now, Blazer aluminum is about the cheapest quality ammo on the market -- its a bit stouter than most in terms of performance. I use it when I can.
I don't particularly like Winchester White Box (Value Pak) ammo, but others here love it. It's a gun thing, I think.
