I'm with
@GLTaylor. To turn a standard 6.5-06 case into an Ackley Improved case, you need to fire form the case to the Ackley chamber before FL resizing with an Ackley die.
You have a two-step process facing you, as the original brass isn't 6.5-06; it's 25-06. So the first step is, in essence, to neck up the 25-06 brass to take a 6.5 bullet; i.e., convert standard 25-06 brass into standard 6.5-06 brass. You can't do this in a 6.5-06 Ackley die. Best would be to expand the neck with a standard 6.5-06 FL or neck sizing die. Then build a fire-forming load that will convert the now-6.5-06 cartridge to the Ackley version when fired in the 6.5-06 Ackley chamber. Only then is your brass ready for FL sizing in an Ackley die.