Given the popularity of "nominal 4mm" Zimmerstutzens from a tremendous variety of low-volume makers in the late 1800's, I've assumed that bore size and rifling varied enough that precision shooting required the ideal size to fit a particular gun. Those Bürger were serious about their accuracy.
Don R.
A modern plastic "tin" of RWS 4mm flobert Cartridges describes them as "4mm lang mit kugel nr. 7"
So maybe the number seven balls are for something as obscure as flobert reloading???
It turns out there was an interesting answer to this and a specific sort of German shooting, a bit like our bell target I guess:
https://de.m.wikipedia.org/wiki/Zimmerstutzen
(In German but you can translate in safari at least, though you do get some comic results, eg apparently the shooting is called “room nozzle”, which I guess sounds better in German)
I have not tried this myself but will certainly now consider anointing my balls before shooting to see if it improves my performanceSome shooters therefore use (sometimes mysterious) means to anoint the balls to improve shooting precision; oiling the balls before shooting is commonplace
Morally flawed
Never helped my shooting much
All explained in this documentary;
https://www.youtube.com/watch?v=oNa1RYgV17o
ATB, ED