From a previous thread here on the IAA Forum is a discussion entitled “Brass suppliers for Polish Cartridges”: viewtopic.php?f=1&t=738
On page 2 of this thread, about half way down the page is this statement and the full post-
" case metal supplier Kynoch (K). "
" xyxy - the feature on Polish 7.9 x 57mm headstamps that I would like to find out the “why” of are the gaps in the segment lines that separate the headstamp into four quarters. These appear on cartridges made by Zaklady Amunicyjne POCISK Sp. Akc., Warszawa (Pk), regardless of case metal supplier, from at least as early as 1926 thru the late 1930s. They consist of either one gap or two gaps in only one of the segment lines on the headstamp, and they can occur in the same year on any one of the lines. There are also rounds in the same years with no gaps in any of the lines. They also appear on a few of the 7.9 x 57s I have that were made by Panstowowa Fabryka Amunicji, Skarzysko (Eagle), but seem to be only in conjunction with the case metal supplier Kynoch (K). these findings are based only on my own collection, so they could be incomplete, although I have over 100 Polish 7.9s in my collection not including those made during the German occupation. Unfortunately, I have not the means to post headstamp photos on this Forum. "
The author information was lost when the site was hacked some years ago.