I just bought a WW2 era rear seam M1 Helmet off of Ebay but i do not know the date it was made. I know that helmets with the stamp between 0-1300 are WW2 era and mine is stamped 1261E. I think it is dated somewhere in 1945 but I am not 100% sure. I also do not have the money to buy the book "Helmets of the ETO". thanks.