Vacuum-moulded and Hot-press formed “Bubble Packs” are common to a whole variety of food manufaturing and packing industries ( Dairy, Condiments, Sauces, Cheese, Yogurt, as is the Hotfoil sealing systems used for the top (rip off) cover.
Usually the packs are made in moderately large sheets, from continuous rolls of Plastic of sufficnet thickness to form the “bubble” without perforating or being too thin, and leaving a stiff border to seal the top on.
Briefly, the Roll of film feeds onto a Mould Block, and under a heating Element array; a clamp seats holding the soft sheet against the (aluminium) Mould, and the air is withdrawn from the mould thru very small Pinholes in the base of the cavities by a strong Vacuum Pump.
The Mould is cooled (may be water cooled by tubes within it) and the plastic hardens as soon as it “bottoms” out in the mould.
The Sheet is guillotined and removed from the mould and stacked up (nested) as the Moulds are slightly tapered, to allow easy removal of the formed “Bubbles” and also stacking.
The cartridges are placed into the Bubbles ( probably 16 or 25 Bubbles are formed in a sheet, maybe more, depending on the machine size);
The seal sheet is placed over the Bubble sheet; sometimes CO2 or other inert gas is introduced by flooding the bubbles, to expel air and moisture, and a Hot grill press comes down and seals the heat sensitive glue in the coversheet into the plastic.
The Sealed Bubble sheet is passed to another press, with set blades, which cut out the individual packets in one pass.
The whole process can be automated ( including the Cartridge orientation and placement), with either Fritz Werner or DWM-type machines as used for filling 15 round packets before or during WW II).
So, in a fully-automated system, rolls of Plastic film, rolls of top seal paper, and loose cartridges are fed in, and the finished packets come out onto a conveyoer belt, to be hand packed into ammo tins ( or in the case of M43 Platzpatrone, into 2,880-round heavy-cardboard Packs.
Knowing the level of technology in DDR, I would say that the individual processes were done mostly by hand, with manually operated machines, which did the “Vacuum” forming, then the filling, then the sealing, then the cutting apart…That is the way I learnt the process back in the 1970s, making our first prototype Single-serve Chutney packs for a trial run in the supermarkets ( didn’t pan out…customers preferred Jars.)
Ten years later, Bubble packs were all the rage, for a very large range of Products, from single-serve Airways meals for Tomato Ketchup, right thru yoghurts, creme-caramel, and other desserts and soft cheeses.
Sayng they were made from “Cheese packing machines” may very well be true, as Cheese Packing in Western Europe was already one use of Vacuum forming in the 1970s; but I would say they copied the technology more likely, not necessarily they bough second hand “cheese packing” machines to convert to packing cartridges.
When I was at S&B, one of their “subsidiary” industries there was the manufacture and sale of Plastic Bag forming and food wrapping machinery, including “Vacuum forming” lines.
It could be that the DDR bought the machinery already set up for Cartridge packing, from S&B Vlasim in the 1980s ( I think the DDR Bubble packs only appeared in the 1980s ( My PP M43 stock is 1985 manuf. date, and I visited S&B in 1993.)
The use of Bubble pack technology for ammo is not unique to DDR; in the 1980s and 90s, the Australian Ammunition factory at Footscray manufactured Feral Control Soft Point 7,62 Ammo ( a 7,62 Jacket of L2A2 dimensions, part formed, and filled with a lead core and formed to a 170 grai SP BT.). These were packed in a five round Bubble pack, in turn packed into a Waterproof Plastic Tray with lid ( stackable) which held some -500 rounds or so.). Same Plastic Trays had been used for packeted Ball ammo ( 40 round packets and one 20 round “Half packet”) ( for training and combat use). The trays held a secondary use as First Aid Kit boxes, wash basins, and sundry other “water-proof” uses…they ( the plastic trays and the bubble packs) only lasted into the 1990s, then disappeared.
I don’t know if any other Military ammo supplier used “Bubble packs” or if many Commercial ammo makers did so…I have seen “Folder” packs ( two half-bubbles bent over and stapled ) for some Japanese? made “House brand” 30/30 ammo ( “S&W brand”)
( I have about five of these Blue print clear “clamshell” packs.).
It seems that for various reasons, the integrity of Bubble packs was not reliable in the long term, was time consuming to open, and the sharp plastic could give nasty razor like-cuts to the fingers…these factors (besides the collapse of the DDR) led to the demise of such packs for ammo.
AV Ballistics ( and former Food (Condiment) Manufacturer and amateur engineer in Food packing)