About 5 years ago I picked up two boxes of .30 AP M2 CHECK AMMUNITION LCOP, they were being sold as common shooting material. One was sealed, while the other had part of the box end missing.
These basic labels were made on a mimeograph machine. The “CHECK AMMUNITION” is across the top of the box. Note how they smeared over the velocity and pressure measurements and hand stamped new values (2711 ft./sec. & 48867 lb./ sq. in.).
Headstamp is L C 4. LCOP = Lake City Ordnance Plant.