Just read Wolfgang Fleischer's excellent
'The Wehrmacht weapons testing ground at Kummersdorf' (schiffer 1997). Reference to quite a bit of testing of concrete artillery shells and even Panzerfaust heads, 105 & 150mm prototype examples for Howitzers manufactured by Preussag-Rudersdorf have been found on the ranges. The structure (from a photograph of a recovered example) appears to be reinforced concrete with a metal cap and driving band with the reinforcing rods running spirally the length of the shell.
I'm sure Sapper has also told us
elsewhere that many German stick grenades his blokes captured at the time had concrete fragmentation sleeves.
Cheers,
Adam.