I'm not going to go through the meaning of DP again as it's already been flogged to death on the site several times but in short, it indicates a rifle that has been relegated to DRILL PURPOSE. Drill in this regard isn't rifle drill or marching (although it can I suppose.....), but it means 'drill' as in weapons training and shooting training/sight setting/aiming, fieldcraft, recruit training, Assault courses............... you know the sort of thing where you can slog the 'drill' rifle to death without harming the real McCoy

Anyone else care to add another few pages......