What is the best definition for runout and the best way to check for runout?

Runout is the straightness of the ammo. If you roll your ammo on a mirror and see the brass neck wobble or bullet tip wobble, you got runout. Little is fine, alot is bad. I dont' like over .004"

I use a sinclaire dial indicator

http://www.sinclairintl.com/cgi-bin/category.cgi?category=REMTCG&item=09-175&type=store

I have been using the "RCBS Case Master Gauging Tool" since the very early 90's. Good luck.

Don't worry about runout unless you have a problem and cannot figure out why.
It can be associated with error in your dies.
Most hunting situations you never need to worry about runout

Runout = Saturday afternoon doing yardwork, someone takes the last beer....you have "runout" and someone needs to 'runout' to the store and get more.

Concentricity of your ammo. Ifyouroll your loaded rounds on a mirror and you can see any 'runout'. Some things that cause runout

neck wall thickness irregularities
bullet seater not set up correctly
case not pushed into the shellholder all the way when seating a bullet

Thanks for replies.

IMO the biggest cause of run out is your expander ball. But then I think the expander ball is the root of all evil in reloading. The expander ball will amplify your run out problem even moreif your neck thickness is not the same.

I think runout begins with the case. It does not matter what you do with the seater die, and how you try to remedy your seating process if you have runout in your brass. Start with taking care of the run out in your brass, and normally the bullet will take care of itself(with a decent seater). Tom.

What does the expander ball do to create runout?

The shoulder is the weakest part of the brass. Some of the brass works up out of the shoulder and into the neck. The expander ball is pulled back through the neck, and when it is, the shoulder is not supported. The expander by it's nature works the brass. If the expander is not perfectly centered(which it rarely is) it pulls off to one side or the other. This pullingis what yields bad run out on the neck. This is also a reason why a lot of people trim the necks, even if they do not have a tight chamber. The more consistent the neck brass thickness, the less sizing will cause run out.

Also a lot of people do not clean the inside of the neck before drawing the expander ball through the neck. This IMO is also a mistake. Dirt can build up in the neck, and on the expander ball. Both will cause a negative effect. A lot of reloaders will polish the expander ball when the get new dies. The polished expander ball will pull more smoothly through the neck, which will have less effect on the neck.

I always remove the expander ball out of my dies. I use the Sinclair neck mandrel. And I only size cleaned brass. It takes an extra step or two. But then I enjoy my reloading. So it is no big deal to me.

I guess you just have to keep in mind that the neck holds the bullet. So if you pull the neck off center just .001, that will have a compounding effect at the end of the bullet. And if the neck is not concentric with the case, well I think you get my point. Tom.