Ive been using std lee 243 theneck diam is .277 for both ,6-06ai neck length is .296,243is.276 so its .020 shorter than 6-06ai .shoulder diam is same for both at .4550, and .4551 resise neck of 6-06ai until you feel the shoulder .this should leave about .020 of the ackley neck unsized. Which has not caused me any problems. If you need to resize the base ,use a 45acp carbide sizer die to get out the bulge at base , if you need to . Use 243w seater as normal.
No brag ,just fact