I was not satisfied with the CZ magazine because for a good work it had to be a tight fit in the ex carcano magazine.
this was meaning the magazine going very hard in and much harder out.take a file and make some space in the carcano magazine until the CZ goes in and out without problem but then it was hanging and don't work anymore - rounds were not taken by the bolt in this position.
it's allways a little between GO and No Go.

there was a promising slit in front of the guide rail

drilled a hole for a 6,3 mm bearing ball so it come out the other side for 2-3 mm

the ball and two springs made from the rest of a mauser magazine spring I used once to make another spring

in action

magazine goes in and out very easy, also when it reach the ball

the CZ magazine have now a perfekt fit

and feeding is 100% flawless if you do it like a man. if you move the bolt in slow motion chance is very high the cartridge tip will not find the way into the chamber because oal of the 7,62x39 is one mm under the distance from the magazine lips to the barrel.