run out question

[bruce moulds]

you can't get better tir loaded ammo than sized (or fired assuming finger seating) brass will allow.
this is the first place to start.
straightening loaded ammo can alter neck tension, however you do it. (or bend the bullet)
brass can have varying neck thickness from side to side, and have a tapered hole when obturated assuming parralell chamber neck walls.
i had this with some 405 win brass, to the extent that a 0.410 bullet would not allow a cartridge to chamber with a bullet seated more than about 0.3" in the case.
the solution came from baco, who were most helpful, because it took a bit of working out, and they just kept helping.
i would add that sinclair said it could not be done, and showed no interest in trying.
an rcbs neck turner with a 41 cal pilot, would perfectly fit cases that were sized, and expanded with a 0.407 baco straight expander.
the 41 cal pilot is 0.405", and when the brass sprung back after expanding, it was perfect on the pilot.
the brass needed sizing so that the expander brought sufficient of the neck internal parralell for the bullet and a bit more.
the necks were then turned to the length of the internal parralell.
knowing the internal chamber diemeter and the bullet diameter is important as this is what you use to establish neck thickness required.
0.000" to 0.004" clearance is worth experimenting with when using lead bullets.
i have turned my brass thickness so i can finger seat with no pressure using unsized cases, and can give a bit of neck tension if i want to size and expand.
because brass is removed from outside the case, it takes a few firings to blow it out so the outside diameter is smooth at bpcr pressures. possibly a stiff smokeless load would do it with more aplomb.
my cases were annealed on a machine using tempilaq prior to doing any of this, in the hope that sizing and expansion would be more consistent.
the outcome of this is that these cases are a custom fit for my rifle, giving consistent neck tension.
a ball anvil micrometer is required to measure neck thickness, and you don't necessarily have to do a full cut on the necks. partial turning is often sufficient.
why it is relevent to this thread, is that runout became minimal.
hope this is of some use to someone.
keep safe,
bruce.