Re: significance in added freebore
For accuracy:
I ordered a reamer from Dave Kiff at PTG.
He wanted to know the bullet I would use, so he could make the throat short enough so I could reach the lands, but long enough so I would not seat into the case neck base doughnut.
For pressure and velocity:
I have overloaded lots of cartridges and found the threshold of short brass life. The longer the bullet is seated, the more powder can be used and stay inside of long brass life. Seated longer and longer, until the bullet jams into the lands. Then the amount of powder that can be used spikes down.
So if I want to set a personal velocity record with some cartridge, I would make the throat so long the bullet cannot reach it.
Roy Weatherby made magnums with very long throats, that made for great velocity, but compromised accuracy.
When I shoot reduced loads in a straight wall cartridge, I can get quiet but powerful loads by seating down into the case. This gets the peak pressure up, even with low gas mass. The 2" long jump to the lands makes the loads very inaccurate, even at 10 yards.