When I reload my .308 Winchester Lapua brass in my Redding Type S neck bushing dies, I free float the decaping rod to reduce runout. This has proven to be effective but I still get as much as .004 in some rounds. I use a Forster runout gauge that suspends the bullet on both ends. When I spin the rounds on my runout gauge I can stop on the high side and press down near the shoulder to message out most runout. I have not tested this to determine if it has a negative impact on the precision of my loads, but I suspect this will loosen the neck tension a little bit. Does anyone know?
Does adjusting runout affect neck tension
- Thread starter texarkanahunter
- Start date
Get rid of the expander ball if you haven't yet. My r/o is -0- without it. .....SEMPER FI!
Shynloco
You can lead a horse to water, but ........
texarkanahunter said:
I'd send that Die back and have it checked by the maker. Something isn't right (IMHO) with that die especially if the decapping rod free floats and is self centering. Even with the expander ball in it (which I also take out) that is a ridiculous runout or perhaps your brass is bad. Just my thoughts. I did that exactly that in the past with one die, only to have the die manufacturer discover that my brass (in that group) was bad - crooked bases.
I, too, would lose the expander ball. You are using the neck bushing to set the sizing of the neck. Nothing else is needed and introduces stress you don't need. I am not familiar with the Forster concentricity gauge. Most that I have seen and used rest the case base and body on ball bearings and then you move the dial indicator to the areas you want to check. I would start by checking the run out of the NECK first, then the bullet. Check that your case neck wall thickness is uniform on the cases in question. If they are not that will introduce bullet runout. ONe other trick is that when seating your bullets, seat them half way, lower the press ram and turn the case about 180 deg. and finish seating. I think you will find that run out is reduced significantly.
Yes it does affect neck tension. A while ago I bought a cartridge alignment tool and decided to straighten a few rounds and save these for the light conditions, big mistake, got a lot of vertical. I played with it on and off and found if you bent bullets back and forth more than once, the neck tension dropped right off. I was running quite a bit of neck tension so I don't know if it will adversely affect those with very light neck tension, such as those who are soft seating.
BigDMT
Floating the expander is one thing, but are you making sure your neck bushing is floating by turning the top screw back out 1/4 turn after inserting the bushing???
If the bushing is squeezed tight in the die, it can easily cause bad runout.
Are you turning your necks??? If not turning your necks with a high quality neck turner you can expect to see bad runout as well.
Are you sizing the entire neck? If only sizing half of the neck, the bottom half could be out of alignment from the factory.
Is your 308 a factory rifle with a factory chamber? Factory chambers can often deform brass.
Are you annealing your brass? It can start to bounce back after sizing once worked too many times.
I'd also recommend removing the expander ball because it defeats the purpose of a neck bushing die by only allowing one neck tension which is only the diameter of the expander.
There is a lot of important info missing here that is needed to correctly identify your problem.
If the bushing is squeezed tight in the die, it can easily cause bad runout.
Are you turning your necks??? If not turning your necks with a high quality neck turner you can expect to see bad runout as well.
Are you sizing the entire neck? If only sizing half of the neck, the bottom half could be out of alignment from the factory.
Is your 308 a factory rifle with a factory chamber? Factory chambers can often deform brass.
Are you annealing your brass? It can start to bounce back after sizing once worked too many times.
I'd also recommend removing the expander ball because it defeats the purpose of a neck bushing die by only allowing one neck tension which is only the diameter of the expander.
There is a lot of important info missing here that is needed to correctly identify your problem.
82boy said:
He's dead on with this question. How many of us have removed a fence post, tent stake, or anything else we've driven into the ground. First thing you do is to wiggle it back and forth to loosen it.
It's best to address the issue before it gets to the checking process. If using a bushing die, make sure that the bushing retainer is loosened about 1/16 of a turn and then locked in place. Start out with straight fire formed brass. Chances are that the fire formed brass that's crooked also has widely varying wall thicknesses.
If you aren't starting with top end brass then at least sort out the best for those loads that you will need total perfection from. For me, the rest get used for sighter/fouler's, or "training rounds" when I take a grandkid to the range.
Problems with these notions,,
You should imagine in this that the greater the tension to overcome, the greater the variance in it. This is not good for all that's going on early in the powder burn toward your tune timing. This is why you should never FL size necks. That is, unless running a peak pressure node up around 75Kpsi in a tiny under-bore. At this point tension matters none, other than to hold the bullet(contain the charge) long enough(not the right amount of time, but at least an amount over .00xxsecs).
So it is possible to increase tension beyond spring back against seated bearing. FL sizing of necks and not expanding them, will do this. Not shooting a 6PPC or 30BR? Don't FL size necks.
So why is neck pre-expansion good? It drives thickness variance outward -away from seating bullet bearing -reducing loaded runout (from one cause). It also leaves brass imbalance biased inward(countering last sizing action). So with time here, neck tension would rise rather than fall. Without expansion last, tension would decrease over time. Something to consider if storage is needed, because you may want it one way or the other. But also this creep is under ~1/2thou, not huge. If recently process annealed, that 1/2thou might mean less. All this is about achieving consistent neck tension, and seating bullets straight.
Button pulling through necks with success takes a plan. I believe forster has worked on the issues.
Another/better plan is to use Sinclair or PMA neck expander mandrels for this specific operation. Their mandrels are already sized right.
You can of course bushing neck size down, without follow-up pre-expansion. If your necks are turned, and your bushings are just right, you can get away with this without detriment.
There are qualifiers, or prices, for everything.
The root cause of case runout is thickness variance. It's brought out by sizing(to cause yielding). With this, if your cases have no thickness variance at any datum & 360deg around, then there is no runout brought into play. So necks do not have to be turned to be straight, and turned necks will not guarantee low runout.
In a broad sense, we should never, ever, size the entire length of necks. There is only bad in it for most. The neck shoulder/donut area of necks will straighten out as well as they will ever on fire-forming. Otherwise, you bring out the demons lurking there.
I wouldn't say often,, have never seen it. Usually, factory or custom, your chamber is your best die.
Tension is not adjusted with bushing size(other than achieving nominal), but with sizing length against seated bearing. Nominal, as recommended by pretty much any bushing die provider, is 2thou under cal(as intended, with any bushing size providing it). This is actually nearly 1thou excess(no big deal) and follow-up expansion would ideally leave necks 1thou under cal. This is with spring back in both directions, and the spring back from ideal 1thou interference fit is all the bullet grip you need, and normally all you will get(regardless of further interference fit). The length of this spring back against bullet bearing is what pressure will overcome to cause bullet release. And also, using your bullets as neck expanders is a bad idea.
You should imagine in this that the greater the tension to overcome, the greater the variance in it. This is not good for all that's going on early in the powder burn toward your tune timing. This is why you should never FL size necks. That is, unless running a peak pressure node up around 75Kpsi in a tiny under-bore. At this point tension matters none, other than to hold the bullet(contain the charge) long enough(not the right amount of time, but at least an amount over .00xxsecs).
So it is possible to increase tension beyond spring back against seated bearing. FL sizing of necks and not expanding them, will do this. Not shooting a 6PPC or 30BR? Don't FL size necks.
So why is neck pre-expansion good? It drives thickness variance outward -away from seating bullet bearing -reducing loaded runout (from one cause). It also leaves brass imbalance biased inward(countering last sizing action). So with time here, neck tension would rise rather than fall. Without expansion last, tension would decrease over time. Something to consider if storage is needed, because you may want it one way or the other. But also this creep is under ~1/2thou, not huge. If recently process annealed, that 1/2thou might mean less. All this is about achieving consistent neck tension, and seating bullets straight.
Button pulling through necks with success takes a plan. I believe forster has worked on the issues.
Another/better plan is to use Sinclair or PMA neck expander mandrels for this specific operation. Their mandrels are already sized right.
You can of course bushing neck size down, without follow-up pre-expansion. If your necks are turned, and your bushings are just right, you can get away with this without detriment.
There are qualifiers, or prices, for everything.
I do not have a tension gage that measures neck tension; all of my tension gages are calibrated in pounds' meaning my necks have bullet hold, I want all the bullet hold I can get. When it comes to reducing run out I want to eliminate all the run out possible before the round is assembled.
F. Guffey
I turn my case necks for 308 Win to .012" and then run the case neck up into a .3075" mandrel. I showed this to a new reloader a while back in my shop and had him run a non-turned case through a regular resize die with the pull through button and when he seated a bullet on both cases....his eyes got rather wide when he seated a turned case that had mandrel treatment! He said...."Man...that's a lot smoother!"
eric n
Silver $$ Contributor
Have you tried shooting the ones that are .004 out against the perfectly concentric ones?What's your avg runout per batch?
I use the same dies w/o the decapper and see a few out of 100 that will be up to .004 but they mostly lie in the .001 range. I used to put the ones with more runout off to the side and use them for fouler and sighters even though I knew for fact I couldn't shoot the difference. Now I check new lots but that's about it.
Edit... I see run out in a loaded round. The brass has 0 runout
Last edited:
My empirical experience also! Or at least pretty darn close to zero most of the time.
shoot4fun
Gold $$ Contributor
While I advocate not using the expander ball for calibers I neck turn brass for I wholeheartedly use it for brass that I do not neck turn. The OP doesn't say but I guess he isn't neck turning. It would seem that the bushing will push any high spots in the outside of the neck in toward where the bullet will be and that will cause runout and inconsistent neck tension. I load 6 Dasher from Gold box Lapua that is turned very slightly. My Whidden FL die utilizes a bushing and an expander ball. These dies produce ammo that regularly measures .001 runout or less.
I've never had anyone, as much as runout is discussed in reloading forums, give an accurate number for what is "too much" runout and I especially have not seen it in this thread. I also haven't seen the OP say just how his ammo shoots with those .004" runout rounds pulled out of the box versus left in. I seriously doubt in his case it will make enough difference for him to measure. Federal GMM is the holy grail of 308 factory fodder. Ever check runout on them? It's bigger than .004".
I've never had anyone, as much as runout is discussed in reloading forums, give an accurate number for what is "too much" runout and I especially have not seen it in this thread. I also haven't seen the OP say just how his ammo shoots with those .004" runout rounds pulled out of the box versus left in. I seriously doubt in his case it will make enough difference for him to measure. Federal GMM is the holy grail of 308 factory fodder. Ever check runout on them? It's bigger than .004".
Can you expand on this Mike? I'm curious just where these loose clearances would be helping us achieve improvements in accuracy?
With all the talk about seating into/off by 0.001" increments, necks turned to wall thickness of +/- 0.0001", neck clearances sometimes requiring lube to get loaded rounds into chambers for firing (kidding on this one), I have to wonder just where looser clearances are of advantage?
My own recent experience with a wildcat 7mm is that a tight throat - spec'd to just 0.0005" over bullet diameter - helps greatly when there's only about 0.080" of neck gripping the bullet and they're seated LONG yet not touching lands so that the bullet's bearing surface ends just before where the neck begins when seated.
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