David TS, It's not a myth but you haven't quite got it right. Boat tail bullets don't stabilize well in rifles that have seen a lot of use with cordite ammo. It has to do with the throat erosion wear pattern caused by the very hot burning cordite. The Mk. 7 and Mk.7z ammo has flat base bullets. The Mk.8z has boat tails for use in machine guns. They won't perform in machine guns either if the barrel has been shot extensively with cordite ammo. I've seen it in the Vickers MMG. They'll keyhole at 100 yards. Brian