Description a little updated here:
https://axarms.com/product/bt-hk-heckler-koch-hk416d-sf-11-sbr-unique-bt-configured-us-exclusive-of-the-coveted-416/
My Aunt’s now deceased long time boyfriend’s dad brought it back from WW1. He sold it to me ~10 years ago for a grand as one of his children had been murdered and the other was a druggie. You can look up the S/N and see it went to France in 1918. I plan to pass it down. Piece of Americana.