Ball Powder ( Spherical granules,of Double base, produced by a Liquid phase colloidal process) was first produced by Olin ( Winchester-Western) prior to WW II, and though used in some ammo during WW II by W-W, but only fully developed for US Military use after the War. It has been in parallel use in US Military ammo with Tubular, single base Powders since the early 1950s, AFAIK.
Since then, many other countries, either under license, or with their own processes, have produced “Ball Powder” for Military and sporting use ( one of the first outside the USA was Israel, with its “IMI-655” Powder of the 1950s, used in , firstly 7,9mm ( 1955, 56) and then 7,62 Nato ( late 1950s onwards). Possibly the “655” denotes “June, 1955” when it was introduced by IMI?
I would say Argentina, being in receipt of US Military Technology, also used "Ball "Powder, having used European “Flake” Powder technology since the early 1900s, brought in from Germany.
Now to the cartridges under examination:
Flakes mixed with ball powder can come from two or three different causes.
(1) Machinery for loading was not properly cleaned out when changing from Flake to Ball Powder, resulting in “Contamination” of the Ball Powder…an inconsequential ( probably) matter wrt loading density.
(2) The Flake was specifically introduced to the Ball Powder to modify its Burning rate or Pressure Curve ( Blending); usually this is done with Powders of different batches, but the same type ( ie, Ball with ball, etc)
Highly unlikely, as the Flakes could jam Powder metering devices designed for the freer flowing Ball Powder.
and Possibly (3), the small quantity was used as a “Marker” to distinguish a particular batch of Ball Powder in Lot Loading and Firing Tests. Again, here, the quantity would have to be miniscule, so as to avoid Powder “bridging” and blocking metering devices, and giving incorrect loads.
AS is known, “Ball” Powders are coated with different Flame retardants ( DNPP etc) which themselves are combustible, but at a slower rate than
Nitro-cellulose or Nitroglycerine ( components of Double Base Powders); also the “spheres” can be flattened as well, to change their surface area, and thus their burning rate.
Ball Powders are used (in different grades) in everything from .22 RF up to .50 cal. So saying the Argentine “Ball Powder” is "similar to Red Dot"
is an assumption without any foundation…Ball Powders cannot be differentiated by their “appearance”, nor even approximately by their shape and size…only by testing by "Pressure Bomb"
and other involved scientific tests, and the results are even then, only approximate, given that Military Powders are Blended to give a certain “Burning rate and pressure gradient”, and then the charge is calculated (per Batch) to give the standard Velocity and pressure in the chosen cartridge…
That way, Charge weights may vary, batch to batch of Powder, as well as Lot to Lot of cartridges ( differances in Bullet Weight over the “nominal” range)
…Bullet-making automatic Weighing machines weigh bullets and group them in batches of a particular weight, sufficient to affect the Powder charge, to give the same Velocity parameters…saw this process done at S&B for 9mm Parabellum projectiles back in 1993.
Anyway, has this “Mixture” of Powder types been seen in a lot of cartridges in a Particular year batch?
Not just one or two cartridges, but hundreds?..for any sort of statistically valid deductions and assumptions to be made about the reason for this “Mix” one would have to sample an entire lot or lots of these cartridges…
Otherwise the most plausible finding is that a minor “contamination” of the Ball Powder occurred either during Blending and or Coating ( large rotating drums, like confectionary coating mixers , are used), or because the Loading machinery ( Most European machinery for loading uses “in-line” Powder feed from Hoppers and rotating or sliding measures, just like Normal handloading, whereas the USA used “Plate Loading” right up till the adoption of SCAMP systems.) was not cleaned out properly when changing Powder types.
Questions to ponder.
Your ammo “Devil’s Advocate”