To quote from List of Changes:
18805 - Shot, Practice, QF, 2-pr, Mark I, /N/ - Steel
The Mark I Practice Shot is made of solid steel, the nose being shaped and turned to represent a fuze.
20161 - Shot, Practice, QF, 2-pr, Mark II /N/ - Steel
The Mark II differs from the Mark I in the cannelure being of greater diameter.
The Mark II was approved in Feb 1917.
The table below, showing make-up of complete rounds, might be of interest
CARTRIDGE, QF, 2-PR, MKS I TO III GUNS, PRACTICE
MARK I [LoC 18848][RL 21719A] Mk I Empty case; No 5 Primer; Mk III Charge; Shot practice Mk I
MARK II [LoC 26114] As MARK I with SHELL, 2-PR, COMMON POINTED MARK II fitted with base plug No 3.
MARK III [LoC 26114] As MARK I with SHELL, 2-PR, COMMON POINTED MARK IV fitted with plug representing fuze 121 or 124
MARK IV [LoC 26114] Differed from MARK III in being fitted with SHOT, PRACTICE, MARK III
MARK V [LoC 26114] As MARK IV WITH CHARGE MARK V
MARK VI [LoC 26114] As MARK III WITH CHARGE MARK V
MARK VII [LoC 26114] AS MARK II WITH CHARGE MARK V
MARK VIII [LoC 26114] AS MARK II WITH CHARGE MARK IV
Unfortunately Naval gun handbooks rarely show ammunition.