The distance pretty much rules out a too heavy recoil spring. I've had a couple of CZ's that came with recoil springs that were far too light, but I wouldn't think that would cause your problem. Still, you never know. Have you tried some factory FMJ ammo? If so, how does it do?
The Lee Factory Crimp Die for straight walled pistol cartridges:
Your substitute for doing it right to begin with.