I was told that one of J&P Customs overseas customers told them the CZ firing pin spring kits for the 452's would work with the Brno no.1 therefore the 1's thru 5's, I knew they were similar but only owning no.1's I wasn't sure. I got two of the 452 springs and tore down my two no.1's and can cheerfully report they work great with the Brno's also.
The upper spring in the photo is the new J&P 452 spring, slighty longer and much more uniform in appearance, the lower spring has only been in this 49 stamped rifle 59 years or so so we can forgive it a kink or two.
In this photo the casing was fired in my 1949 stamped no.1 at the range last week, the indent from that firing is on the left side of the case, the upper indent is after replacing the firing pin spring. Hopefully from the photo you can tell there is a very considerable increase in the indent, this should mean better ignition and hopefully better accuracy. I hope to range test both rifles in the near future, but feel the newer spring is worthwhile from a reliability stand point if nothing else.