It doesn't make any difference what bullet diameter you use; 0.450" , 0.451", or 0.452" . The flared case mouth has to accept the base of the bullet. Then there is the issue of consistent case length which causes different amounts of case flare.

Don't over think the problem. Adjust the case flaring die so the shortest case has enough flare to start the largest diameter bullet. Flaring the case mouth does not require ±0.0005" accuracy. ±0.010" diameter on the edge of the case mouth is more than close enough.

The bullet should enter the flared case mouth at least 0.020" to 0.030" to prevent bullet or case mouth damage when seating bullets.

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S&WHF 366