Help identifying cartridge

Hi,

Another cartridge case found in a Hampshire, England field. The headstamp appears to read (clockwise from 9 o’clock) ; “40 17 f BK” . Looks like .50 cal size cartridge.

Thanks

This is a German 20x82RR MG FF case made in 1940.

BK is a factory code used by Luftwaffe for a short time, assigned to Hugo Schneider AG (HASAG) at Altenburg.
Lot 17, sublot f, of 1940.

Thanks guys that is very interesting.