Is that a ww2 liner?

[greatwhite]

Some of the webbing maybe period but the liner is post war i have one too.

[plumbob]

it is a strange one. there is a theory that some of these may have been made with surplus midwar "A" washers or war time sweatbands/nape straps . which makes sense using up old stock. your one appears to have OD3 webbing as well never noticed that before on any. perhaps they were using some of this up as well. The 5 1 in the crown denotes that the shell was made in 1951.