I am going to guess the date on the picture is wrong because from what I can see that is a flat NEW gastrap - everything just looks 'right' and even the gas cylinder still has 100% finish (which is unheard of). I just can't see anything that refines the date further - do we have any uniform afficianados that can date things better from what can be seen.

With nothing more, my guess is that the rifle dates the picture to 1937 to 1939 and the date given is wrong. Either that or someone had a flat new gastrap that they kept in a closet for a dozen years...