I have shot a bunch-0-bullets in various 6mm rifles with 9-1/8 and 10" twist ,,,(all various factory bbls.) I found a threshold of good/bad accuracy to be at length of 1.100" and BC of .430 ,,,any longer or higher BC gave poor accuracy ,,,,,I didnt read this in any book/manual,,,,it has been realized over 50 years of trial and error,,,,with a 10" twist I feel the best bullet for accuracy and retained energy while using bbls with ~10" is the Berger 87gr VLD...this twist will shoot 100 gr sierra sbt's but the 87 vld has higher muzzel vel and more retained velocity downrange and more retained energy,,,,Roger