A step in the case with a sharp corner? Concentration of stress with a 35,000 psi miniature explosion sounds like a recipe for disaster.

One-piece brass and steel metallic cartridge cases have traditionally been made from strip stock material, whereas a round disc is “punched-out” from strip material and formed into a cup. Cups are then fed into vertical stamping/draw presses, with various other operations performed throughout the process, and through a combination of drawing, metal forming, annealing and cutting operations, the finished shell case component is produced. This has been the traditional method for producing straight-wall cases, typically used for pistol and rimmed handgun cases. Necked rifle cases are produced using the same basic method, but there are additional steps inserted along the way to produce the longer case length, and to neck/bottle and trim the case toward the end of the process.

The link to the video in the previous post shows a process where the operations are performed at different work stations. This does allow the manufacturer to inspect the components at various steps along the way, but also requires additional handling of the component. My perception is that the general user community, whether they are commercial loaders at some level of volume, or the “home” reloader on a much smaller scale, feel that this particular manufacturer produces a quality product, so this process obviously serves them well.

Within the realm of this same basic method for producing cases from strip and cup, other manufacturers perform these same basic operations, but they use multi-station transfer presses to perform more operations in one work station. With this method the cup is fed into the press and does not drop off until more steps are completed. This approach is generally felt to be more efficient, but it brings a higher level of complexity to that work station.

Different manufacturers today incorporate this process of production with various combinations of steps and work stations, with a wide variety of equipment, but it appears that they all utilize the strip/cup method in their facilities for much, if not all of their case component production.

Regarding the “forced extrusion method”, as noted in the previous post, I am assuming that this is a reference to a newer method which starts from round “rod” (more specifically, coiled wire) rather than cups. This incoming wire is sized according to the size of the case being produced, but is generally approaching the diameter of the finished case. This method of shell case production utilizes an entirely different forming sequence and equipment set, and in general terms, is referred to as a heading process. This is done on a high-speed, precision, multi-die machine, and the configuration is different than that of a draw press. This is the same process used to produce the majority of fasteners today, as used in the automotive, commercial, appliance, agricultural, and construction industries.

While the example of the “stepped” 9mm case blank was most likely produced using a heading method, this step feature on the ID is not typical of this process. The heading method of producing cases has been in use for many years now, and a notable percentage of pistol cases are now produced using the heading method.

As is the case with any manufacturing process in general, focus on detail at each step is critical to success.

Technology in manufacturing continues to evolve, as does design for new configurations of case construction and projectiles. As noted in the previous post, we are seeing more two-piece cases today, with varying combinations of materials, with a goal to produce lighter cases. It will be interesting to see where this ends up.

But, to confirm what has already been stated to Q, your examples were not intended to be “two-piece” cases, you just had the unfortunate experience to have them end up that way. As a home reloader, I discard any of these which I happen to come across, if for no other reason than the reduced case volume.

I don't bother to sort out the "stepped" cases.
I have not had a separation, I do not generate a bulge by seating 135-147 gr bullets, and I didn't get but a 13 fps increase from "lower volume."

CAVEAT: I don't average a lot of reloads on my 9mm brass, because I only pick up empties at practice; match brass stays behind because I am usually ready for lunch by the end. Maybe if I were a dedicated brass rat, I would wear some out.