I have very little reference material on these types of helmets and my understanding is that BMB manufactured all of the P-type shells.
The shell appears to have started its life with a coat of brown Khaki paint this is evident from the interior of the shell so it was very probably produced in and around mid 1943 the exterior has been repainted in a textured charcoal grey which IMO is war time applied as I have been able to find reference to this type of texturing found on the Canadian issued Steel Mk I's in Lucy's book tin lids and a few other sources.
I know from other research that British post war RCAC Mk I's can be found with a heavy textured OD green paint but can find little data on it's Canadian cousin
The liner is a 1942 I.T.C. in a size 6 1/4 it is missing one of it's buffers but is still quite soft a supple the chinstrap is an early Mk III and is correct to this helmet there is period evidence that supports these can be found worn with the standard Mk II chinstrap as well as seen worn by Canadian troops in Italy or Southwestern Europe.
Any comments and opinions on this Mk I and the textured paint on the exterior of the shell are most welcome thanks for looking.