M1 helmet production date - Can't read stamp - any advice?

[jcp]

Any tips to help read the stamped number on the M1 helmet?  I see the S for Schlueter but interested in finding production date. I assume cleaning or scrubbing the helmet is not recommended. I can read the Firestone liner logo and number but not the helmet.

[earlymb]

You could try to rub it with some WD40 or some chalk to see if that improves contrast?

[aef1917]

Production dates for WWII M1 helmet lots are not known outside of a tiny handful that have been found in period documents.  The charts you see online are educated guesswork based largely on the observable physical attributes (fixed loop, front seam, stainless rim, etc.) of a relatively small sample size of helmets.  Messing around with a helmet to find the lot number is a fool's errand at best and often causes irreversible damage.  Don't do it.