I have what I think is an early French 7.62 x 51mm NATO experimental Armour Piercing load. It’s headstamped TE 54 with a NATO symbol. The bullet has an unusual rough surface and appears to have been plated with zinc or similar. The casemouth has a dark purple seal but there is no black tip as I would have expected with AP. Can anybody confirm that this is AP and ideally tell me the full military designation?