We know about production ammunition by polish firm Zakłady Amunicyjne “Pocisk” S.A. for civil used:
- shotshell for hunting &sporting - c.1924 produced only case without eleboration, c.1926/7 making full elaborating ammo
- .22 rimfire from c.1927 (first was introduced for production .22 Krótki (short) in the next years was produced .22 Długi (long) and .22 Długi Precyzyjny (long rifle)
- 6,35mm & 7,65mm Browning - startedproduction in c. 1935
But I don’t have anything information in polish source about production this headstamps probably used on revolver ammo caliber .320 (I was found in internet only two trace for this).