Hey Rowdy - I just "slugged" the step area with an oversize lead bullet - the step is smooth BUT it seems tight.
I seated one of my .460 bullets at SAMMI Max 2.55 rather than at the crimp ring 2.51, knowing full well it would wedge in the bore. I coloured the bullet with a red sharpie marker and then slid it in to the chamber and slowly, with constant pressure, closed the breech.
Well, I got a good image of what's going on in there. The "step" area is tight. The rifling started to faintly show up at 0.06" at which point the measurement is .458". At roughly half way it is .459" - I measured 2.46" from the bolt face which was close to half way along the mark. Where SAMMI indicates .465" (basic?) I have .459" at this point.
Looks like I'm just living with a tight 'step'. The smaller sizer I've ordered should eliminate (touch wood) the problem.
Imagine buying a new rifle that isn't within SAMMI specs for the chamber. I feel a rant coming on!
Edit - I've adjusted my loads down in powder and seated the bullets deeper, crimping on the nose and this seems to be the best solution if I want to keep .460 size (which I do). I'll still try out the smaller sizer for the halibut but I don't think the smaller diameter bullet could match the accuracy of the .460s.