Strange head stamp on PzB41 case

[Hoeksel]

Today I found 2 very bad 2,8 cm PzB41 shell cases and I was allowed to only trade 1, so I took the one with a weird stamp. I knew I have seen these before, and there is a thread on a German site, but no clear answers.

Head stamp is (12/3/6/9-o-clock):

PN66f
M
/38
P

So it is Polte manufacture from 1938, but no WaA and what is this PN66f? On the German thread there where 3 examples:

PN66e and 2 x PN66f, all three P and M, /38 and /39, no WaA

Any clues anyone?

EDIT: my digicam is away for repair so no pics, sorry!

 

[Hoeksel]

From a former German ammo collector I have heard that PN followed by a number and a letter are Polte drawing numbers. This might indicate these PzB41 cases are from the experimental stage which makes it an very interesting case even if it is not that good!

 

[Tmine35]

I have copy of Polte experimental case drawings list from 1943. For this case it gives drawing numbers 28 H - 25 A 6780 and 28 H - 24 A 6561 ( new type ? ), Correspondingly it gives Polte catalogue numbers 228 and 228a.
However numbering systematics of experimental case seems to be quite wild and yours may well be an earlier drawing number.