The comments about loaded cartridge runout in a previous thread got me thinking about this again.
Over he next while I'll start threads about die set up and a few others and we can share our suggestions and experiences and learn from others and discuss how we have overcome some of these challenges. Honestly for hunting ammunition out to 200m I will often only check things if there seems to be a problem and many of you may share this view and see little point in this exercise. To each their own...
I will start with my thoughts on setting up a regular sizing die for minimal run-out. This will not discuss how much to size a fired case. The suggestions below are for a regular FL or NS die, but would not apply to a Lee Collet (neck sizing) die for example.
The ideas are not original and come from information shared on other forums and Glen Zediker's excellent book for example.
When I started chasing accuracy I pursued many of these topics relentlessly. I will add that I'm not sure that I could consistently see a difference on the target between ammo with a .002" compared to a .004" measured runout (on loaded cartridges). There is some argument about how guys read the runout, i.e. whether you need to halve what the dial says. I am simply talking about the dial on my runout indicator fluctuating by that amount i.e. the needle moves that amount in total over the course of a full revolution of the cartridge.
What we are trying to achieve is to get the die square in the press, or actually to ensure that the case is sized straight. Runout on a sized case should be very low as a seated bullet adds another area for run out to creep in. For accuracy I like my sized cases to not exceed about .002".
One way to improve runout is to allow the shellholder to float - i.e. removing the clip on the press ram. That way the case centers itself in the sizer die as it is resized. This actually did make a difference and this is how I load on a single stage press. Bear in mind that the Forster Co-Ax sort of tries to do the same by floating components. The idea here is that the floating case sorts out some of the alignment issues between the ram (i.e. shellholder) and the sizing die.
Another way is to float the dies as well. Some guys set things up so that they have a hole at the top of the press and a hole in the lock ring and place a pin through the holes, so the the die can be prevented from screwing in or out, but can float. There is a great deal of slop on die and press threads and lock ring threads. Feel how much a die can wiggle about in the press if not locked down. The problem is that it is extremely simple to lock down a die cocked to one side, given the slop between die and press and die and lock ring. Another way is simply to mark the die and the lock ring and keep an eye on the alignment as you go, without locking the die right down. Yet another is to insert an O-ring under the lock ring, to allow a degree of movement. A Lee lockring actually allows a little bit of movement if you don't screw it right down.
If you like the lockring idea and want to get the die square there are a few possible ways to do this. One way to square up the die is to put pressure on the die from below whilst sizing a case when you lock the lock ring. In other words a case from below will push the die up in the threads and square it (in theory). Another is to have the bottom of the die in hard contact with the shellholder, but this assumes precise machining of both shellholder and dies. Redding provides thicker shellholders (competition shellholder sets) for this purpose and as a means to adjust headspace by swapping back and forth (as the hard contact and press camming over slightly can adjust headspace with shellholder thickness), but the heights didn't seem to work with any of my other brands of dies as the lengths of the sizing die body and the shellholders don't work together.
Yet another way suggested is to use machined shims either to set up the dies, or to actually use (with a hole through the center) when sizing cases, in other words you would put the case in the shellholder and place the shim / washer over the case and then size it with the bottom of the die making hard contact with the top of the washer when sizing. This requires precise machining to achieve the appropriate resizing and can require turning down the die and again it assumes that a lot of things are machined square to begin with.
The problem is that whenever I locked a lockring and removed the sized case / took pressure off the die from below etc. I could not unscrew the die. I've never had the flat sided lock rings like Hornady to try, so this may sort that out as I could use a wrench to get it loose. Any thoughts on this? Anyhow, as a result I moved towards the floating shellholder and die not locked tight, or with an O-ring as my solution. This works well for me.
Many blame the expander ball for pulling case necks out of alignment. This is certainly true and I did measure a few scenarios. The problem is that dies size too much, so without an expander ball in place, neck tension is too high. That is unless you use bushing dies, or have the dies honed to the prefect size for your firearm and your components, specifically the neck thickness of your brass. Forster does precision honed dies by the way. The other problem is that unless your brass is of high quality with regard to consistency of neck thickness, the inside diameter of the sized case will be off-center as you sized the outside and not the inside diameter and essentially pushed the imperfections to the inside. Given all of that, an expander ball is not always a bad thing.
I favour Forster dies, but haven't managed to find them for all the calibres I load. The Forster expander is unique in a few ways. The ball floats on the stem and the stem floats as there is a rubber O-ring under the expander stem lockring. Furthermore it is set up so hat the expander ball sits very high in the die and the case neck is still supported by the die as the case begins to contact the expander ball. This helps to keep things lined up; well that is the theory anyway and they seem to work pretty well to me.
Fortunately you can set up an RCBS die to do exactly the same (this I first saw discussed by Kirby Allen). What you do is to size a case and leave the ram at the top (i.e. the press handle right the way down) case in the die. Then you screw up the expander stem, until you feel the expander ball contact the bottom of the case neck. Then you screw it back in (i.e. the expander ball deepr into the case a full turn or so). Now you have achieved similar support for the case when the expander ball enters the case neck as the case is pulled down over the expander basll as a Forster die would achieve. The expander stem will no longer deprime cases, but I am strongly of the opinion hat this is a separate operation anyway prior to cleaning cases. You can then also choose not to lock down the expander stem tightly as a Forster, or you can lock it down by raising the press handle and stopping when the expander ball is in the neck of a case and locking it there where it is hopefully centered.
Set up like this my RCBS dies have generally performed very well.
By the way, Lee dies use a very long "expander (ball)" which can also be set up to achieve the same.
Set up like this and floating the in the press results are generally excellent with most brands.
Some brands of dies do not permit this type of set up, Redding being an example, as the threaded portion of the expander stem is insufficient to permit screwing it up so high inside the die.
I always use a good lube when resizing and prefer Imperial Sizing Was (now sold by Redding on the body of the case) and use Redding's dry graphite lube for the neck. This keeps lube out of the neck and off the case shoulder and helps prevent the dies from gumming up.
I hope that this adds value or introduces some new ideas. I'm interested to hear of the ideas that others use to minimise runout from sizing. I will discuss how I set up dies for determining how much to resize next.
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