The following is the answer to this quiz:
Ordnance wanted testing done as a finish on the M1 Garand using Pentrate. Testing showed that it came out "somewhat shiney". More testing was done on this finish because "Springfield Armory was having a fit about the use of Parkerizing as a finish for small arms weapons." But that's another quiz.
My sites with data and books and CD for sale. These are commercial sites. They also have Ordnance Data files posted there.
ps could use some hits on the sites