The most accurate way to verify what the die is setting the neck inside diameter is to measure the widest part of the easy x expander on the decapping pin as the neck diameter is the same as the easy x expander.
The bullet you select should be a thousandth (.001") larger than the neck ID, and you typically would not be able to start flat base bullets into the neck by hand. Flat base projectiles are very commonly used with this cartridge. I would also recommend chamfering the inside of the necks for easier and straighter seating if using these flat base projectiles.
