What exactly is "run-out?" I always thought that it was the measured variations one would find (COAL, etc.) within a batch of cartridges he reloaded, but is that the case?
John

You get a little gadget on which you put you reloaded bullet. The back goes into a V and so does the tip of the bullet. The bullet can now roll around it's own axle. With a dial meter you measure the amount the bullet wobles around the axis. The measurement is taken on the bullet where it is seated in the case, some take it on the brass, but that will add the amount af variation on the thickness of the brass. Hope you understand and get the picture.

What is important when measuring the runout is that you must sort your cases in A & B cases.
A cases are cases with a difference in neck wall thickness of less than .0001", the rest is B. If the variation is more than .0003", I throw them away.

The idea is to get your loaded cartridges as centre as possible.

Maybe I've been doing this wrong. I put the head of the case in one pillow, and the shoulder in the second pillow, then measure the runout (often TIR, for total indicated runout)on the bullet at the back end of the ogive.

I'm not sure it makes a lot of difference if you are looking for comparisons with your own product. However, if you are comparing your results with those of others, then you might be talking apples and oranges. In any case, the idea is to shoot arrows, not bananas. Using my method, very good loads will measure .001-.003".

Info from others on this will be welcome.

RCBS makes a tool for this, and it's OK, but I'm sure there are better ones available.

Brice I am sure you meant pillar and not pillow, a pillow won't give you much stability.

The rest is what it is supossed to be.

In lathes, engines, brakes, etc, people talk about measuring run out.
It is how out of round something acts when turned.


If something is slowly turned while a dial indicator is touching it, the change on the dial is the runout.

Sinclair's book says to measure the mid neck of the case with reference to the body.

I like to measure the ogive of the bullet in loaded ammo with reference to the body.

When I say, "with reference to", I mean that is the part that acts as the bearing surface on which the case turns.

The importance of runout is that if a bullet enters the bore out of alignment, then the center of mass is off center of the bore. That center of mass is spun by the rifling and when the bullet exits, the bullet moves in the direction of the center of mass. The faster the twist, the more error.

Supposedly, according to an old NRA article, .004" runout causes about 1" error at 100 yards. The same article claims that the data tracks the prediction.

Concentric objects share the same center, axis or origin with one inside the other. Circles, tubes, cylindrical shafts, disks, and spheres may be concentric. Concentric objects do not have the same radius.



In geometry, coaxial means that two or more forms which share a common axis; it is the three-dimensional linear analog of "concentric".

Looks like I was way off.

Runout----That's what you do when the little lady produces the "honey-do" list.

I thought runout was what happens when you spend too much money on shooting & reloading supplies...

Do yourself a favor and forget you ever heard the term "runout".....it'll drive you nuts and after a lot of buying of gadgets and gizmos you'll finally believe it's nothing but a gimmick....a myth...nothing to get excited about!