The author of some of the best sources of information on CZ 75 history released his latest book, "CZ 75 Pribeh ceske legendy" (Story of a Czech Legend) by David Pazdera in the Fall of last year. This one has more detailed information on the building, testing and serial numbering than the earlier works. It is in Czech so requires the use of an e-translator and some knowledge of the language to work through the odd translations that can show up. This makes for a very slow read of the book but hopefully, correct translation. There is about a page length of mention on the Spanish cast frames.
Most of the frames for the short rails were forged. CZ started moving to casting of the frames in 1978 but had made only 200 at year-end. With its cast frame production capacity of only about 200 a month, the company sought to add capacity from another source. Some negotiations on production of pistols outside of Czechoslovakia had already started in 1977 between Merkuria (Czechoslovak exporter) and the Spanish company, Alfa in Eiba. An agreement was concluded in 1979 with Alfa to produce cast frames to augment UB production. In March 1979, tests on Spanish frames revealed cracks that were also observed on UB cast frames. It resulted in the decision to beef up the frame and slide for the second generation design. With this design change, the new Spanish frames first arrived in January 1980. While this co-operation did not meet expectations, it did help CZ significantly increase production in the early 80s. By the mid-80s, CZ had ceased to use the Spanish source.
This would seem to indicate: The cracking issue was related to the cast versus forged frames used for the short rails starting at the end of 1978. Spanish frames were not used in short rail production. There is no mention of the disposition of the fewer cast frame pistols made before the cracking issue was discovered in early 1979.
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