Neck Runout

[Mavrick79]

What can I do to improve the run out of my necks after resizing?

.308
Lapua Brass
Redding full length size die with expander ball
Imperial sizing wax
Forster Coax press
Sinclair run out/concentricity gauge/dial indicator

I bought the brass brand new and fired it once in my Tikka T3. I checked the run out on the necks after firing it and they all came out pretty much perfect, none were over .001 run out. After resizing the run out on the necks are all over the place, from .001 or less up to .010. The only thing I was able to do to improve this was to run the brass through the resizer several times, I know this is not a good practice as it overworks the brass. I assume my problem is the expander ball pulling the neck off center.

I am not neck turning at this point and would like suggestions on what my next step should be to improve this. My goal is to improve the consistency of my reloads.

[Bart B.]

Expander balls do bend case necks.

Straightest necks on resized fired cases come out of full length sizing dies whose neck diameter is a couple thousandths smaller than a loaded round's neck diameter. They're the only die type that has its sizing surfaces concentric with each other and keeps the fired case body, shoulder and neck aligned when they're reduced a few thousandths of an inch. Neck sizing dies don't keep the case body fixed in alignment with their necks; they don't even touch the fired case body enough to size it down.

Four choices:

1. Buy RCBS Gold Medal full length or Redding S-type full length bushing dies and bushings of the desired size(s).

2. Order a Forster full length sizing die then have them hone its neck out to some diameter you specify for an extra 10 bucks.

3. Have a local 'smith hone out your own full length sizing die.

4. Keep using your existing die and expander ball, but run a bore brush chucked up in an electric drill inside the fired case mouths before decapping (in a separate die) and cleaning them. That'll reduce the friction of the ball against the case mouth and typically bends them less. Set the expander ball up as follows:

___a. Set the sizing die in the press as you desire, then back up the decapping rod up until the decapping pin's well above the case bottom.

___b. Run a case all the way up into the die, then back up the decapping rod until the expander ball stops against the inside of the case at the mouth/shoulder juncture.

___c. Screw the decapping rod about 3 turns down so the expander ball's a bit lower.

___d. Lower the ram bringing the case about 1/32nd inch out of the die, then stop. Back the decapping stem up until it stops against the case, then tighten it.

This centers the epxander ball decently in the case mouth. When you lower the ram, the case neck stays in the die's neck while the expander ball enlarges the sized down case mouth and neck bending is typically reduced by the case neck being held tightly in the die neck.

Neck wall thickness spread of .001" is good enough. It's not necessary to get them all perfect as you'll probably only see the difference of .010 MOA if you shoot your stuff into no worse than .100 MOA at any range.

[cryogenic419]

+1 on the Redding Type S FL dies

[Mavrick79]

Thanks Bart, I'll give that a try with my existing die. I think I'm also going to get a type S full length bushing die.

I've heard that with the bushing dies its best to size the necks down in stages using a larger bushing then going to a smaller one. Is there any merit to that?

[Bart B.]

I've never heard of sizing in steps. Nor do I think it's needed

However, there's no end to what some reloaders think of to make their stuff better. A lot of ideas are marvelous or better.

[Mavrick79]

It seems like it would make sense to do it in steps to reduce how much the brass is stretched when its sized down.

[Bart B.]

Note the case body also stretches moving the case shoulder forward in full length sizing dies. It stops when the die shoulder pushes the case shoulder back during the last several thousandths into the die the case makes.

Cases shorten when they're fired. In one test reloading the same .308 Win case 47 times with max lodes, it shortened about .003" when fired then grew about .0037" after full length sizing. After it grew to about 2.010", I trimmed it back to 2.000". It grew about .0007" each shoot and size cycle.

Take a few fired cases and size each one in multiple steps; one in 1 step, next one in 2, then 3, 4 and 5 steps. I'd start with the die backed up to where the case neck just barely starts into the die's neck. One turn of the die down lowers it 1/14th inch. The case necks's about 3/10ths inch long. You can figure out how much to move the die for each case for how much each one grows to its complete full length sized case length. Then you'll know if your reasoning is valid. Post the results for all to see.

[zeke]

And hopefully you are already insuring the inside forming portion of the die is squared up to the brass you are resizing.

[Mavrick79]

Bart I was talking about starting out with a large bushing then going to a smaller and smaller one until I reach my desired neck diameter when using a Redding S die or any other brand bushing die. The idea was to bring the neck diameter down in steps in an attempt to not bend the neck. I've never done it and don't even have an S die yet but have only read about it. I wasn't referring to bumping the shoulder back.

Zeke, the Forster Coax press allows the die and case to float to self center.

[Bart B.]

Mavrick, thanks for the clarification.

I don't think sizing down the complete neck in small increments will help. Its thin side stays the thin side regardless and that's what offsets the mouth center from the outside neck center. But even with .002" to .003" bullet runout from neck runout half that much, good ammo in good rifles will still shoot no worse than 1/4 MOA at short range, 1/2 MOA at medium range and 3/4 MOA at long range. That's as good as what centerfire rifles can do.

There's enough clearance in shell holders to let the case center in the die as it starts to be sized down. One top ranked competitor told me years ago he liked the ram on his ancient RCBS Jr. press being loose in its frame and had over 1/16th inch of slop in its movement at the top of its stroke. That let even tight fitting cases in his shellholders perfectly center in his dies. Decent presses have their critical parts well aligned anyway; they'll stay that way if properly maintained.

Really straight case necks and bullets are down to about 8th on a list of 10 things mandatory for best accuracy, in my opinion.

[jepp2]

The idea was to bring the neck diameter down in steps in an attempt to not bend the neck.

Your brass, your die, your choice. But my experience with using Redding S dies with bushings is they aren't going to bend the neck. Bushings aren't cheap. You will probably wind up with several near your final neck OD sizing to accommodate different neck thickness with brass you size (can vary by manufacturer, and lot). You may also wish to vary your neck tension.

My suggestion would be to size without the expander or get the carbide expander link. Even with the carbide expander I still lightly lube the inside of the neck. So smooth when the expander pulls back through. And if you do use the expander, set it up as Bart suggested.

Redding has some excellent tech support. You might benefit by giving them a call about using multiple bushing steps to improve neck straightness.