cw308,
When you show 0.451 or -.452, I am assuming you made the measurement with a caliper limited to that resolution. I know a lot of folks use calipers for this, but I think with bullet diameters and related measurements, like slug measurements, it is worth having a micrometer with a vernier scale for resolving tenths of a thousandth. They aren't expensive. CDCO Machinery has them starting at $17. With the vernier type, just check the reading at zero to subtract from your measurements. If you want to spend more money on an electronic digital one, Harbor Freight has one for $35 that will work well enough. The digital ones typically resolve half of a tenth of a thousandth (50 millionths). Not necessary for this application, as a fifth or even a third of a thousandth would be close enough with bullets, but it provides some pointless but pleasing degree of satisfaction to see all those decimal places.
Anyway, I am saying I'm not sure exactly what you have, but the step should be bigger than the bullet and the rest equal-to or smaller than the bullet. Equal-to works because the brass typically springs back 0.001" from expansion and that is enough to hold a bullet.
Real Gun,
That's a good resource you linked to. Thank you.