12.7x99 blank M1A1 by HFL

I just came across this ammo box (in the web) with factory/lot code “HFL” but can not find it in any NATO code manufacturer list.

Does anybody know who this manufacturer/entity is?

Belted ammunition is often getting functional lot numbers when several loads are belted and/or could be from various manufacturers.
As these are all blanks I wonder if this still could be a functional lot when it got repacked in a depot or other military facilities.