Jim, I have made a few dies, bushings, neck expanders, balls etc from high carbon steel down to mild steel, heat hardened and non. The only ones that I have seen wear out are softer steel expander irons and balls. Carbon in different forms can be very hard (eg diamonds) or act as a lubricant (some graphite forms). In fact we add carbon to the steel to make it harder in the heat treating process. The heat treating process at certain temperatures and cooling then allows the carbon to take a "hard" but brittle carbon form (martensite)layered within the interstitial structure of the iron. In the powder and primer residues you get both. Some gritty hard stuff and some nice soft lubricant (small enough particle size and correct structure to "slide"). Those of you who clean shells with ultrasonic will know the issues with removing the carbon lubricant on outside and inside of neck. Most reloaders wipe outside of necks clean (removing large "gritty" lumps" and some lubricate the inside of neclks with a brush etc which also removes the large lumps. BUT if you have clean brass on steel with a lubricant it is very hard to wear out the die. Personally I now harden the expander irons but not neck bushings or dies.johara1 said:
What a great thread. Some different approaches to getting low runout. all obviously work for the user. Some of these require some machining knowledge. Others don't. I suspect the cheapest and easiest to employ for the bulk and those who don't want to muck around with neck tension (or have settled on what they want) is the Forster option of honing out the die to your requirements (other die makers also offer this option.) Those who want to use adjustable neck tension there are some great tips on Germans thread that should see you get under 1 thou runout too. A perfect world would see a die that matches your chamber and there are great suggestions here to do this.
In trying to get all this knowledge back to the original question. It seems to me fairly common thought that runout is caused by too much brass movement, (exagerated by varitaitons in neck wall thickness etc). Generally in the neck, or full length sizing stage but can be caused at bullet seating if you have a lot of neck tension. Best ways to alleviate this are dies that do little work and "align" things well and neck turning. Alternatavely ditch the brass that doesn't give you minimum runout in your dies.
What's the old saying - "measure twice cut once"
