Are you sure the WCC 81 isn't Mk.7z? It's usually Mk.8z that will keyhole if the throat erosion in the barrel is well cut with cordite Mk.7. The best surplus I've ever had was FNM 71 Portuguese MK.7z. We tested it all for accuracy and nothing else held a candle to it. I bought 10,000 rounds from Century Arms when they had it. I still use it for test firing rifles here.