run out question

[bruce moulds]

you have good runout figures.
it doesn't get better than 0.002 or less.
if you shoot a number of groups 0.002 or less against 0.008, it would be interesting to see if you can tell the difference, assuming total honesty.
keep safe,
bruce.

[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.

[chaneylake]

being just under 4 years into this, you have totally lost me

[bruce moulds]

chaney,
don't panic. it takes a bit of thinking and having a go to come to grips with.
i only mentioned it on reading that you had gone to the trouble of getting a runout gauge, suggesting that you were really into runout.
holding them and squeezing them and reading the wind are much more pressing issues.
when you light the fire, the first thing that happens is that the bullet bumps up to whatever space it is in.
if this happens to be off centre, out of line, or reverse taper, you will not achieve accuracy potential.
with bullets seated in the case, they bump up to case diameter and shape.
if this is consistent from case to case it is better.
another way to overcome this is to breach seat the bullet into the rifling (freebore) as scheutzen guys do, or come close by seating a bore diameter (pp) bullet only 1/8" in the case, leaving the bullet with no runout in relation to the axis of the bore.
by neckturning you are creating a brass freebore in exact alignment with the chamber, which we hope is in alignment with the bore where chamber and bore join, but might not be.
keep safe,
bruce.

[chaneylake]

now this I can understand, thank you so much for the extra reply

[Tombstone 71]

Thank you for posting that info bruce, I am running hornady 405 brass in my 40-70 and have found the same thing, although now I know how fix the problem


Tim

[bruce moulds]

tim,
aint that the good thing about forums.
we can all save others by passing on some learning.
keep safe,
bruce.