I came across an unadvertised storage unit sale today . It was marked $10.00 - I offered $8.00 -sold . It's in really nice condition . It has the rear seam (shucks) so I think it's post WW2 .
Not necessarily post war. Rear seam, swivel bale M1 helmets were used during WW2. True they were used for many years after that. A quick glance at the liner showing the back strap with snaps for a nape strap tells me that yours is pre 1960 since the nape strap disappeared around that date. A little investigating on the name inside will also help date it's actual use. Here are a couple links for you to help date your liner. Top Pots - U.S. World War II Restored Airborne and Infantry Helmets