Am loading once fired brass (batch of 50 Winchester) out of a Remington M700 in .308 Winchester.
Measuring runout with a Sinclair runout gauge.
Runout started at half a thousandth to 1.5 thousandths right out of the chamber. Sized them with a Lee Collet die. Most ran 1 thousandths to 3 thousandths neck runout. There were a few that ran more than that, but I culled them out. All were inside chamfered.
I seated 168 SMK's using a Redding competition seating die. A few had really good bullet runout 2-3 thousandths, but the norm was 3-5 thousandths. Some ran really high....like 8-10 thousandths. A couple was like 12-15, but I pulled the bullet, resized the case and reseated, and was left with 7 thousandths for that one....
How in the world can a case that starts with 1-2 thousandths neck runout, end up with 5-8 and sometimes greater bullet runout when seated with a precision die like the Redding Competition seater???
Is it varying inside neck thickness? I understood that was pushed to the outside when sized with the collet die, and would show up in neck runout?
Is better brass like Lapua the answer? I could neck turn, but I have a factory rifle, and understood that neck turning could have negative effects in a loose chamber.
Does Redding have any choices for the seating stem (the cup that pushes against the tip of the bullet). If so I have found on some dies that getting a stem that fits the profile of the tip of the bullet can make a big difference.
Hornady makes stems that fit their A-max line of bullets and they work really really well with plastic tipped and vld type bullets.
I seat the bullet 1/3 of the way, rotate the case a ways, seat another 1/3, rotate again and final seat.
When I was having problems with runout, after much help from the guys here and a LOT of searching, I found that my shell holder was crooked. A new shell holder fixed the problem. I never knew I had a problem until I started checking runout. Sometimes the gun would shoot really good groups, and other times not so good. I thought it was a problem with the gun, but it turned out to be a problem with the loading process.
There are a number of things that can cause runout. The first, you've discovered is the neck thickness. This is pretty well taken care of by using the Lee collet die.
I'll list a few things that are easy to check and fix, each of these items are things I have found can lead to larger runout. These aren't my ideas, I've just 'collected' them over the years.
1) Float your shell holder. If you still have the spring clip that holds your shell holder in place, get rid of it. Either use your press without anything holding your shellholder in place, or put a small rubber band or O-ring around the slot to hold it in place. I don't use anything to hold the shellholder in place. This change will allow your shellholder to self center as the cartridge goes up into the die.
2) Be gentle. When you are resizing and when you are seating your bullet, be gentle with your stroke. I don't do the stroke all at once, I let off the pressure as the cartridge starts into the die, so the shell holder can center itself. Also, I use nice even pressure as I seat the bullet.
3) Chamfer your brass, this lets the bullet start into the brass with less initial force. The larger force can push the neck and cause neck runout.
4) Lightly clean/polish the inside of your necks with a brush wrapped in steel wool. I put an undersized cleaning brush in my drill press, wrap it with a little bit of 0000 steel wool and lightly polish/clean the inside of my brass necks. I run the drill press on it's slowest speed. This gives me more consistent neck pressure and more consistent feel while seating bullets.
5) Make sure the seating stem on your seating die is touching the bullet all the way around and not bottoming out on the tip of the bullet. You'll probably need to take your seating die apart to check this.
6) I used to seat the bullet in 1/3's and then spin it a bit and seat the next 1/3 of the way, then spin it and seat it the rest of the way. I don't do this any more with my good seating dies. With my old standard seaters (cheapy RCBS stuff), I still do this.
Those are the simple ones. I'd highly recommend the book by Zediker about reloading for competition. Zediker Publishing
If some is good and more is better, then too much is just right.
My mind is a raging torrent, flooded with rivulets of thought, cascading into a waterfall of creative alternatives
Well, it's really hard to be sure from here but we can try.
First, I wonder how long you have used the gage, and how you are using it and how you are intrepreting it.
Taking the last first, maybe I can cut your runtout in half immediately. I can't imagine any case sent through a Reddiing (or Forster) seater can exit with .015" of real run out (RO). You do understand that what you see on the gage is called Total Indicated Runout (TIR) and that the actual RO is only half of TIR?
No seater can correct for a bent neck. With the Sinclair tool, I think neck RO is taken near the mouth while the body supported at the base and just below the shoulder, right? So, RO mostly shows how much out of alignment the neck is to the centerline of the body. Very little of that RO comes from the seater, per se, so hopeful efforts to correct by seating part way, turning and completing seating isn't really going to do much good.
Consider that if a neck were 1 1/2" long and you took one reading at the present location, then a second near the outer end, the second reading would be much greater simply because the angle of error shows more difference the further away from the start of the error it's read. The anglular error would be unchanged but the TIR would appear greater. Meaning, if we carefully push a bullet perfectly straight nto a slightly bent neck, the dial indicater will swing further when we measure off the tip simply because it's reading further out. If that's what you are seeing, understand that the "real runout" remains only that of the bent neck AND only half of the TIR, and it's due to the bent neck, not so much the seater.
Most sizing dies and chambers are perfectly straight, or nearly so. But, pulling a largely unsupported expander out of a totally unsupported case neck almost guarantees the necks will be pulled out of perfect alignment, each time we size/expand them. All factory case necks have thicker:thinner sides. The thinner side will give way, stretching more than the thicker so the neck CL will tend to drift as the expander is withdrawn.
Obviously any angular difference between the between the center lines of the inside diameter (ID) and outside diameter (OD) of a pipe/neck can't be corrected with a die. Nor is alignment likely to be correctable with a reamer. Reamers make the necks thinner but they tend to follow the existing hole while doing it.
Concentricity out of the seating die requries that the inside, not the outside, of the neck be concentric and no conventional die can assure that. Correcting that requres outside neck turning as the best way to improve the neck ID and OD centerlines.
That starts with obtainly the best possible necks before turning.
Obtaining a sized but still straight neck is best done with a Lee Collet Neck sizer die. I've also found the Lyman "M" die expander used with a stripped FL die to be a close second. That's because the M expander it pushes IN, instead of pulling OUT as conventional ball expander does. Neither is die is magic, they can't fully correct for all of the neck's error but using either is MUCH better than a conventional sizer/expander.
When the inside of the necks are as straight as you can make them, turn the outside to (try) to make the outsides match the innerds. Turning neck for factory chambers has limited value, don't bother skinning off more than perhaps 70-80% of the circumference. The Forster Hand Operated Turner (HOT 100) is the least expensive, easy to use neck turner with a carbide cutter and micrometer type adjustment knob I know of. It's NOT "BR" grade but it is plenty good for factory chambers; try it.
Conclusion; Concentricity requires good necks, good necks requires fairly good brass that's very well selected and prepped. All any good seater can add is to not destroy what the case prepping has done.
I don't agree with generalizing TIR-vs-R(cutting TIR in half) because your runout cause would first have to be determind before going there. For example, if your runout is caused by big variance in thickness, this will be indicated regardless of centerline conditions. And in this case, your runout would be exactly as indicated(provided that is your only contributer).
Also it would be pretty rare that a positive variance will be followed by an exactly opposite negative variance with brass, because that would mean only one specific contributer, with no others combining in the abstract. That's not reality in my experience.
I also do not follow the collet die as a runout reducer idea. I just don't see how it would. What I see, is that it would contribute less towards additional runout. And as you have seen for yourself, it did not reduce runout.
You did not mention which Sinclair runout gauge you're using. I hope it's a standard V-block/bearing type. If not all bets are off.
If it is, then I would be very concerned about that initial runout measured right out of the chamber(before sizing). There should be essentially zero TIR on the necks at this time. If not, you've got an ugly chamber flaw(unlikely), or very high thickness variance in your brass, -producing bananas.
Don't assume any particular brand of brass is better in this regard. It varies from lot to lot in all of them.