I have a couple of hundred soldier letters and have several that appear to have been written with "Lead" pencils. The higher friction with lead affects the writing a great deal. Letter sets that I have with flowing cursive ink writing and penmanship - turn into blocky printed letters with faint markings when it appears that a lead pencil was used - only to turn back into flowing penmanship when he could get a pen and some ink.
I have also dug a couple of these pounded "Pencils" in Arkansas out of campsites.
Thanks - hope that this is of use - Gene