Another Frame Question

[ArtS]

Since my first post the other day turned out to be one of those unknown mysteries, I thought I would try another beginners question.

Here is a picture of one of the guns I showed the other day. It is a DH (grade 3) and documented as such by a letter. Barrels on this 1901 gun are Damascus.

I thought that the grade on Damascus guns pretty much was a function of barrel quality and the overall finish was tied to this. Here is a shot of the barrel flats on this gun.

The larger 3 I am sure is the unstruck weight (for 3 pounds even), which would be consistent with the gun weight. I believe the smaller 3 to the right is the grade. I have no idea on the C. My question is, do the D and 4 on the left signify the Damascus grade? I raise this question because the barrels appear to be 4 Croille (sp?). In the barrel picture, it looks to my untrained eye like there are 3 full rows and 1/2 row on each edge. I bought a GH from 1906 and the grade 2 gun lookes to have only 3 row Damascus, yet both barrels have the same designation on the rib. Both barrels are numbered to their frames. Any comment on what these mean?