British, known as a 'turtle shell'. Used in 1945 and post-war.
Looks to have been painted green over black.
You may find some info on the liner straps.........
I've checked and all I can find is only the size. The liner came out pretty easy, but I didn't see anything under there either.
Try looking for stamp marks in the steel around the chinstrap area. They may be faint due to the paint covering them. They may be in different places too.
It's a "turtle shell" as Walkwolf said, yours was possibly made around 1945, but I think it would have been made much later, at a guess 1950's and it is unlikely it saw service in WW2.
If the deal was that it is a WW2 helmet, he still owes you money I think!
Is that black or dark green on the inside.
My earlier example is a dark green from the factory.
Horrible helmets, I was first issued one when I first joined up lol not very comfy or practical!
Oh yes too true lol
We used to have to tie strips of sandbag to ours for cam and to break up the outline of the helmet, it looked like a sandbag wig, only problem is for a laugh the lads used to light the rear of it whilst on parade (if wearing them) and you would end up with a hot flaming mass on your head lol