Neil, young Matty's Father on this forum gave me three 6.9mm Dewalt drill bits recently, and agree they do the business.. I just bought five 6.9mm HSS Drill Bits from Axminster, it is surprising what a difference that 0.1mm does to reduce the gap between blank and tube ... 
Maurice, i don't have a bad word about the Colt drills, especially when using them with Acrylic ... 