.303 blank
It is a "Cartridge S.A. Blank .303 inch , with mock bullet, Mark VI", introduced by List of Change Paragraph 11317 dated 1st November 1902.
The idea was that it would feed through the magazine rifle better than either the earlier paper bulleted blanks or the short crimped Mark V blank.
The Mark VI consisted of a normal short rosette crimped blank over which was crimped a thin brass mock bullet. The body of the blank should be blackened for identification. The headstamp is probably "R (arrow)L C II", indicating it has been made from a converted Cordite Ball Mark II round made by Royal Laboratory, Woolwich.. However, it may have been made by any of the contemporary makers, Kynoch,(K), Kings Norton (KN), Greenwood & Batley (GB), Birmingham Metals (B) etc.
It was not very successful, as often the mock bullet blew off and became stuck in the rifle bore, or at worst the mock bullet left the barrel and injured a soldier. In 1906 the Navy received permission to remove the mock bullets and in 1907 the army followed suit. It then became "Cartridge S.A. Blank .303 inch , with mock bullet removed, Mark VI".
After all were used up, production reverted to the Mark V which continued in use until after WW2.
If there are other items that you need identifying, post them here and I and others will do what we can to help.
Regards
TonyE