I believe it has more to do with the rod dragging on the CZ ejectors than the bores actually being too tight, although the "tight bore" story is all over the net.
This, plus the fact that manufacturers tend to make jags too large in diameter, especially in the smaller calibers. As others have noted, .20 cleaning accessories are just about ideal for a .22 rimfire bore. Brushes have to fit the bore, so I made my own adapter so that I can use a .22 nylon bore brush on my .20 rod, but you can buy adapters from outfits like Brownell's.
Paul
