I recently returned from Normandy and got this ground dug helmet from someone who was clearing a building site. It looks to be a 1935 model as it has the turned edge rim. It’s in very poor condition due to corrosion but it has a very interesting bit of damage as can be seen from the photo. It looks like a large caliber round went straight in the front and straight out of the back.

I’ve only included a photo of the front but the hole in the back (the exit hole?) looks almost identical-it’s not bigger or jagged as one might expect from an exit hole. Both holes measure approximately 1.75cm across, so it’s not a .50 cal.

I was wondering if 1.75cm matches with anything that was used around D-Day? I’m guessing whatever round it is was armor-piercing as it still had the velocity to punch straight out the back leaving a clean, undeformed hole?

Any information would be gratefully received!