50 bmg berdan primed brass

I picked up some berdan primed 50 bmg brass. 50 at 12, R at 9, D at 3, and 56 at 6. I looked thru my books and couldn’t ID it. What is it?

This was produced by Armeria F. A. San Cristobal, Dominican Republic.

What is the meaning of dates 50 and 56?

To what I know:
50 = caliber .50
56 = production year