Jay, I'm sure your .271 neck will work just fine as I have clients using the old .272 neck with "blue box cases" who have taken the time to tune for the difference in neck thickness, they all report getting tiny groups.
I'm very busy in the shop and dont have the time to work up new loads for my 6mm BRX before the NBRSA 1,000 Yard Nationals so I will use my old cases with my previously worked up load.
Tommy Leroy Johnson