My education in 'Military Studies' was the study of the logistics of the major combatants of WW2. Logistics wins the wars. Ammunition for all WW2 combatants is a true interesting study as from around 1935 to 45 the small arms as well as ammunition evolved faster than the ability to supply the forces with the correct round for the correct weapons.
Germany was known for standardization and still had several variations of the 7.92X57 out there, as well as 7.92Kurz, 9mm, and some weapons had very specific ammunition requirements, but still units got the wrong ammo now and then. The Soviets had issues with the 7.62X25, since the PPsH needed a cartridge with a little more propellant to function properly, and if you put that same cartridge in the TT33 pistol 'bad' things could happen. The standard 7.62X54R also went through many changes as the 'needs' changed.
The British .303 was very weapon specific, you could not use the .303 Mk8 in the Lee/Enfield rifle, or Bren, only the Vickers MMG. The Vickers could fire the standard .303 rifle round but frequent weapon stoppages resulted. So if you got the wrong ammo...bad day.
True on the coding, I call it the 'fantasy' of wargaming, the Hollywood perception over actual applications.