Lyman, as you know, uses a universal receiver to do their testing for the .270 Win. and the OAL they come up with is what works best in their receiver. Looking at the Hornady Loading manual, their C.O.L. for the same bullet, 150 gr. SP #2740, is 3.210".
Their testing for the .270 Win. is with a Winchester Model 70.
Got to remember that these numbers are guidelines, provided by these tests. Your results will vary.
Bill