Interesting. I guess you do know that there are people selling fake M21 s/a - which are actually fairly obviously not right. The most obvious fault is that the rivets are all very large flat-headed ones.
However I think that yours is essentially right - its a genuine shell, but I believe the liner has been changed. I think that only because it looks too new. It is the same pattern of liner and chinstrap as the original, so it would be impossible to say that it is 'wrong' as it could have been renewed any time in the last many decades, put into storage and simply not used since then.
There is one oddity - the rivet at the side should have a ventilation hole down its centre. It looks like yours does not have that. That doesn't make it 'wrong' necessarily - it is possible that when the liner was renewed there were none of the correct aeration rivets to hand.
I will say that I am not an expert in Spanish helmets, so I may be wrong. But I do have one of these, unquestionably genuine, so I know the look of it. In fact I'd say your shell is more authentic than mine, as it still has its badge bracket and is what I believe to be the original brown colour.
Oh, hold on, wait a minute. Sometimes I do not know what I am saying. Obviously the M21 s/a did NOT have the Franco-era badge bracket originally, these were added *after* the end of the Spanish Civil War, seemingly in 1943 according to more than one authority, thus well after the helmet was originally put into service. I knew that, honest.
But here's something new. It seems, many helmets were reconditioned about that time (mid 1940s) and the replacement of the original hollow chinstrap rivet (as shown on mine above) with a simple flat-headed rivet (as on 3aStalina's) is fairly common and well known (except to me, as I have only just found out about it). But even so the rivets are not so absurdly big as those used on the recent reproductions.
See, I told you I wasn't an expert.
those are both very nice examples of the Spanish M21
it kind of reminds me of the Portuguese M40
It is remarkably similar to the Portuguese M40, that's true. Though not by any means identical. From what I understand and observe the M40 more closely resembles a Japanese export product known as the Kobe helmet, which the Portuguese trialled in the 1930s. That Kobe helmet is similar in some ways to the well-known Japanese M30 (see here - .: World War Helmets - Casque Modèle 30 "Kobe" :. ) but it was never taken into full service. The Portuguese were obviously familiar with the Spanish helmets of the period and it seems that their choice of what to eventually produce locally was influenced by the Japanese and the early M21 (the sin ala). There's next to no hard evidence for this, as usual, but we can make reasonable inferences based on what others have theorised and the evidence before our eyes. And change the story if more knowledge becomes available, of course!
thanks for your replies! to me the M21 sin ala reminds me of the roaring '20's women's hat styles. for example,