Help: Need to know the meaning of a code prefix on 8.8cm 39/43 Konigstiger projectile

[hassiman]

I have here a rare German 8.8cm KonigsTiger /PaK 43 projectile that is stamped with the code Bczw.
czw = Freitaler Stahlindustrie GmbH, Freital /Sachsen
B = ?

The prefix in front of the 3 letter code stands for the kind of material the shell was made of. usually one of 3 letters, either A, B or C are prefix codes found on AP shells.

A means: nickel free steel

B Means ????

C means: cylindrical shell body with steel nose welded on it (Verbundgeschoss).

Can anyone find mention of what the code prefix B means?

Thanks,

Rich