I put in my vote for .270 Ackley improved. I got my dies from rcbs.
My 270 Ackley improved is a chromemoly 29 inch McGowan 1.250 taper to 1 inch. I was reading on another sight about barrel manufactures. They list all the top 8 and they all use about the same machinery. But little things like correct break in.......... goes a long ways in barrel life and accuracy. They also had doubt's about cryogenically treated barrels.
The things I like about my AI is: I probably should have got stainless, but I don't mind carrying a gun hunting that weights 16 or so pounds with my 8.5 pound barrel, Harris tall bipods, and 6X24 power 56mm scope. My gun is 11:1 twist which is optimal for .277 and 140 grain bullets. What is so nice in heavy target guns is the recoil is so low and straight back that you never come off of the target. on 24X I can see the holes appear on paper up to 200 yards. Out hunting you see where the bullets hits.
I have never recoved a 140 SPBT from any animal they even went clear through elk. neck/spine shots completly removed a vertebrae or two, the chest shots nice exit wounds.
Chronoed very accurate loads @3320 + or minus 6 fps with 61.2 grains of IMR 7828 CCI 250 mag primer. Moly coated Sierra 140 spbt