Your cartridge, (please note the terminology here. It isn't a 'bullet shell' !), is a 20mm Hispano-suiza round and almost certainly fired by an aircraft, not by a ground based weapon. Cartridges from ground based 20mm weapons, usually Oerlikons, are different to this cartridge. The letters are the manufacturer, Radway Green, in 1952 and the 20mm you can take a guess at yourself !
You other brass item appears to be part of an large calibre shell nose fuze. What markings has it got on it ?
RRPG