free bore = throat.
bullet jump = proj. distance to contact w/ leade

Here is the correct description and location of the leade and throat:

About Free bore

From a machinists perspective (including reamer manufacturers), free bore starts at the case mouth and is measured forwards to the rifling.

From a shooters perspective, free bore refers to bullet jump, measured from the ogive of the projectile forwards.

Same term, two completely different uses of the term.

Going into a bit more depth (for those who want a headache):

Reamer manufacturers use the terms free bore and lead (or leade) interchangeably. In other words, free bore and lead both refer to the area from the case mouth to the beginning of the rifling taper.

Reamer manufacturers use the term throat to describe the ogive shaped part of the reamer. This describes the length of the taper before it comes into contact with the projectile. The throat of a chamber has two important measurements (to the reamer maker), length and angle.

Try not to dwell on this as it can be confusing for industry outsiders. Reamer makers such as PTG are very smart in that if you as a consumer say that you want a long throated cartridge, they translate this into meaning a long free bore cartridge and will work towards this goal accordingly.

A throating reamer cuts both lead and throat angle.

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