Look at that, a Short butt, I have one ever seen two of those fitted during my time, rather uncommon pieces.

---------- Post added at 08:56 AM ---------- Previous post was at 08:51 AM ----------

In the same photo of the close up of the butt marking, I notice there is a raised ridge that runs from the rear takedown pin to the stock trunnion, that must be a new lower receiver group update by Diemaco. I don't recall that ridge, on my issued rifles, but will have to go back and check some photos I have. An interesting little design evolution.