Definition of bullet runout

[lrgoodger]

My understanding of bullet run-out is that technically, it is HALF of the full swing on the dial indicator when using the Sinclair concentricity gauge. That's because the gauge is short of the bullet center line by the same distance at the maximum reading that it is at the minimum reading in the position 180 degrees away from the maximum. So, actual run-out from the bullet center line is only half of the full swing on the dial.

That means the full box of 50 rounds I mentioned in another thread as all having less than .001" run-out actually all had less than .0005" run-out, and my average of .0015" is actually an average of .00075"!

I seldom go through this thinking process when talking about run-out, and habitually quote the full dial swing as my run-out. How many others are guilty of this?

Ron

 

[DUSTY NOGGIN]

i always assume , most people state the diameter/full dial swing when they have problems with it , but then state radial measurement when they are trying to feel better about their measurements

i measure everything full dial swing so those are the numbers i use ,may as well just you the number your tools are telling you

in the end, 0 runout would be the same for both

 

[BoydAllen]

I use the full swing, as do most of the people that I know. If you mean something other than that, you should explain that, every time that you write or speak on the subject.

 

[Daddymac]

TIR Total Indicated Runout, if it ain't zero it's what's on the dial. Yes, technically from the center line you can have .0005 per side, but one will be negative and one will be positive for a total of .001 use what the tool is giving you, it's much easier that way.

 

[dgeesaman]

I always assumed it was full indicator movement. Diametral.

Given that bullets are very round and necks are turned, the radial runout is basically half of that number.

I don’t use the term “total” runout because that is technically a measurement of runout executed over a length of cylinder. Not something we do here but I’m anal retentive like that.

 

[Straightshooter1]

I've thought about that too in that actual run out seems to me to be half the full swing. But, I've never seen anyone refer to it that way. Since I try to get as close to -0- as possible I don't give it much thought any more. I do set my dial to where -0- is in the middle of the swing as I look for that -0- run out. But since people will typically state the full run out, I will state the same so there's no confusion as to what I'm getting.

 

[dcali]

I always use full swing. But I think an equally important distinction that is seldom made is whether or not we are talking about radial or axial runout.

Radial runout is when the axis of the bullet is parallel to the axis of rotation, but offset - it will measure the same no matter where you measure.

Axial runout is when the axis of the bullet is tipped relative to the axis of rotation. This will differ depending on where you measure.

In reality a little of both is likely present, but if one person is measuring a cartridge at the bullet tip when another is measuring at the case mouth, they're not comparing apples to apples.

 

[Straightshooter1]

I always use full swing. But I think an equally important distinction that is seldom made is whether or not we are talking about radial or axial runout.

Radial runout is when the axis of the bullet is parallel to the axis of rotation, but offset - it will measure the same no matter where you measure.

Axial runout is when the axis of the bullet is tipped relative to the axis of rotation. This will differ depending on where you measure.

In reality a little of both is likely present, but if one person is measuring a cartridge at the bullet tip when another is measuring at the case mouth, they're not comparing apples to apples.

Good point!

Does everyone measure at the ojive? I assume most do, but there are variations on equipment design that are different. I have and like using the Sinclair concentricity tool as apposed Hornady's tool that measures the from base to tip. I never like Hornady's set up as it doesn't line up to the case's length as the case would line up within a chamber, therefore the run out reading would not give you what you would see within a chamber. Any thoughts about that?

 

[rardoin]

I define it as the last handful of bullets in a given lot...when I am about to 'runout'.

 

[Dusty Stevens]

I define it as the last handful of bullets in a given lot...when I am about to 'runout'.

Like when the husband comes home is what i relate it to. I dont have a gauge for that.

 

[rardoin]

Like when the husband comes home is what i relate it to. I dont have a gauge for that.

Gimme' three steps, gimme' three steps mister and you'll never see me no mo'....LOL

 

[T-shooter]

I like to measure about halfway to the tip. If there is runout it is easier to see here. I can usually keep over half at .001" or below on the dial (.0005" from the centerline), and usually a few at up to .003" on the dial. Remember all bullets aren't exactly round. I have see Hornady, Sierra, and Berger as much as .0003" out of round on the bearing surface and I read Berger's tolerance is .0003".

 

[Kurz]

Can you measure my run out for me, please?

This is from one of Ryan's posts about the 300 Norma Mag ammo he bought...

 

[dogdude]

Can you measure my run out for me, please?

This is from one of Ryan's posts about the 300 Norma Mag ammo he bought...

That's just a little more than ZERO !

 

[Straightshooter1]

Can you measure my run out for me, please?

This is from one of Ryan's posts about the 300 Norma Mag ammo he bought...

Isn't that a cartridge designed for shooting around corners?

 

[rardoin]

Isn't that a cartridge designed for shooting around corners?

It was loaded with 20MOA for a rifle with a '0'deg rail. You do have to be careful and index it properly to get the most gain....

 

[dgeesaman]

In reality a little of both is likely present, but if one person is measuring a cartridge at the bullet tip when another is measuring at the case mouth, they're not comparing apples to apples.

In fact apples, oranges, and bullets have one thing in common: lots of curved surfaces. We just need to be exceedingly careful to stick with well defined terminology and define it when no such things exist.

Fortunately a picture is worth a bunch of words, so it would be wise for all of us to grab a snapshot to go with their “runout posts”. Just like a good day shooting: pics or it didn’t happen.

 

[mikecr]

My understanding of bullet run-out is that technically, it is HALF of the full swing on the dial indicator when using the Sinclair concentricity gauge.

!. You don't measure 'bullet' runout with that gauge. You can measure along case and loaded cartridge(off loaded bullets).
!!. Sinclair calls it a concentricity gauge, but it's not. In no way does it measure about any center line axis. It's a runout gauge, with readings including everything out of straight(TIR). Truly, the only time your ammo is really straight is when it reads so on this type of gauge (v-block type).
!!!. While reading off loaded bullet noses you're including more than TIR. The slightest case head out of square would read as high variance on the gauge (amplified false runout). Unless looking for this, it's best to read TIR on bullet bearing just in front of case mouths.
!!!!. Concentricity itself is misused here in that what we read, our deviation, is eccentricity.
Concentric (legit spelling) is achieved with eccentricity removed (the associated +/- you're describing).
!!!!!. Loaded ammo can be gauged at concentric even while shaped like Marilyn Monroe.
But straight ammo is also and always concentric. It's a really big difference.

 

[Uncle Ed]

Below the top image is how the cartridge is held in the Hornady concentricity gauge. The problem with the Hornady gauge is you can not check case neck runout because it spins the cartridge on the bullet tip. And the bottom image is for cartridges that spin on the case body.

Bottom line, if you want to make concentric ammo you need to check case neck runout after sizing. And find out at what step in the reloading process any runout is induced.

I also find that the Redding neck thickness gauge is good to have if a expander is used during sizing.

With case necks with neck thickness variations I subtract the variation from the total neck runout when not neck turning. And the Redding bushing die FAQ tells you to use the expander if the necks vary more than .002.

Below the expander will push the neck variations to the outside of the neck. So checking neck runout need to be compensated for.

 

[mikecr]

With case necks with neck thickness variations I subtract the variation from the total neck runout when not neck turning.

Really? You do this?
Have you engraved measured thickness variance onto each case(or some other system), so that you can do this subtraction on measuring runout off them necks?
I must be misunderstanding you.

Seems easier to measure loaded runout off bullet bearing, removing said thickness variance from reading.
You are right about the neck benders though(like the Hornady). They do not show much of actual runout.