I have an update.
There was significant resistance on bolt close, so I decided to size the brass using Forster FL sizing die. These were the results:
With the expander ball out, neck size of .262
With the ball in, neck size of .267
The neck after seating the projectile is: .268
It seems like 0.268-0.262 = .006, too much tension
On the other hand, .001, too little tension.
Is this correct? Too little and too much tension? I have been told to go for .002 of tension.
The other option is, I fl size the and then use a neck size only with bushing, but wouldn't that be working the brass neck twice?
Or, can I safely go with the .001 tension?
Thank you
I'd say .006 is way too much even for a cartridge with a neck thickness of .012" or even for something less. There a few things that that's at work with a good "neck tension" that work. .001" can work just fine in a bolt gun, but one may not want to use mag feeding as recoil may cause the bullets in the mag to change seating depth during firing. With a 6mm Dasher, there may not be recoil to be of concern, but an issue not to be ignored. In addition to this, the size of the bullet and how far it's seated into the case contributes with this issue.
There are some shooters who've used almost zero neck tension so when they chamber their round, which is hand fed, the bullet is pressed into the lands and the bullet also pushes into the case. Their reasoning is that they get very consistent velocities this way and don't have to worry about throat erosion. So, having little or no neck tension isn't really "dangerous", but it could be a problem if you have to eject a live round where the bullet is pulled out of the case and the powder spills into you're trigger assembly.
In my .308 I've gotten good results with .0015 neck tension and have had no problem. . . though as I mentioned, I'm hand feeding those cartridges.
The only issue I have with using an expander ball in my Forster FL sizing dies is that the ball pulls on the neck causing the shoulder to change its headspace measurement and makes for less neck runout. This can be mitigated if the amount of reduction is reduced. Like your necks are .262 with no expander ball and the ball will expand it by .005" and if you have the reamed where the die only reduces them to .265, there's less tending to pull on the shoulders and less tendency to induce a lot of runout.
You don't have to size twice with a bushing die as you can control the amount the necks are being reduced before the ball is pulled through. But busing dies just tend to produce more runout than a FL sizing die that uses not bushing.
