Hi chaps,in an armourer issue years ago,J Carlin mentions that there seem to be a few 37mm COW gun cases around which have grooves machined about half way up the case. Ive just got one with said grooves of which there are 3. Is this trench art?? OR is it a service addition to differentiate between the COW gun ammo at 37mm and 40mm 2pdr ammo? The cow gun was used as a stop gap in WW2,just a thought but ive seen a fair few now,any ideas? They could be removed to leave a mint case,as it was cheap. Cheers in advance.Tig.(No pics as camera on strike!)