PS and FS code on RUAG ammunition boxes

The Swiss RUAG company uses the code letters PS and FS code letters -followed by a 4-digit number- on some of its box labels to indicate the lot numbers.
As far as I’ve understood PS means something like Probe/Prototyp Serie, and FS means Fertigung Serie.
Can any of the German members please explain the difference between Prototyp and Fertigung?

It’s confusing to me because Prototyp means of course ‘experimental’, and Fertigung should mean ‘production’.
However, I’ve seen both SF and FS codes ONLY on boxes of experimental cartridges. Why does RUAG place FS codes on boxes that contain experimental cartridges?

can you show a pic from the 2 stamps (and give the calibers involved) …so I can ask Mr.Keim in the RUAG Archiv?

Thx
Peter

I have never seen a Swiss Box with SF , FS means Funktions Serie

MY mistake, sorry! I should have written “PS and FS codes”

Peter, thanks for your offer! However, the pictures from Gyrojet show exactly what I ment.

“Funktions Serie”. Now it makes more sense to me.
Is the next step in cartridge development after a Probeserie the Funktionsserie? In other words: First stage is the prototype and second the functioning stage?