Case/Bullet Run-out: How Big a Deal Is It?

[Mikecr]

There is a difference between Thickness variance, Runout, and Concentricity, that seems to be getting muddled around.

Sinclair's ball mic(either with a stand, NOT the cheap indicator version), checks thickness variance of the brass at the necks. The percentage of variance there runs full length.
This shows up with each cycling of the brass(firing/sizing), as growing runout that can never be fixed. First stage of my brass culling.

Sinclair's 'concentricity' gage is really a 'Runout' gage(and the best of em). It measures any and all runout irregardless of overall centerline. Your cartridge is not STRAIGHT until measured so on a Sinclair.

The true concentricity gages(like the H&H), measure w/resp to a pinned centerline. This shows only how concentric a loaded cartridge is. They DO NOT measure runout, and in fact mask most of it.

A cartridge can be concentric and still have a great deal of runout. But if a cartridge is straight(no runout), it is concentric as well.
Given this, and all the ways a cartidge can rest and point in a chamber, I believe STRAIGHT is as good as it gets.
This is what you should strive for.

 

[Moman]

There is a difference between Thickness variance, Runout, and Concentricity, that seems to be getting muddled around.

Sinclair's ball mic(either with a stand, NOT the cheap indicator version), checks thickness variance of the brass at the necks. The percentage of variance there runs full length.
This shows up with each cycling of the brass(firing/sizing), as growing runout that can never be fixed. First stage of my brass culling.

Agreed. Makes sense.

Sinclair's 'concentricity' gage is really a 'Runout' gage(and the best of em). It measures any and all runout irregardless of overall centerline. Your cartridge is not STRAIGHT until measured so on a Sinclair.

Agreed. Haven't used this particular tool but will probably own one before too long.

The true concentricity gages(like the H&H), measure w/resp to a pinned centerline. This shows only how concentric a loaded cartridge is. They DO NOT measure runout, and in fact mask most of it.

This is where you start to lose me.

A cartridge can be concentric and still have a great deal of runout. But if a cartridge is straight(no runout), it is concentric as well.
Given this, and all the ways a cartidge can rest and point in a chamber, I believe STRAIGHT is as good as it gets.
This is what you should strive for.

Mikecr, can you go a little further with the last explanation? Most of this makes complete sense, but I start to lose you when you say a cartridge can be concentric and still have runout. I always considered them to be one in the same.

 

[Mikecr]

Well as a simple example, a perfectly concentric cartridge might have thickness variance in it's neck(pushed outward) that could be measured or discarded as runout.
Concentricity is variance only from a centerline. So to see this case as actually concentric you would just move your indicator away from the known thickness variance(noise).
Also the case could be a complete banana and still be measured as concentric, if you pin both ends and indicate nearest one(often the bullet tip).
Doesn't make it straight of course, but it is 'centered' in measurement.

In a sense, if your bullets are jammed, your chamber is big & sloppy, and your boltface is square, concentric would work just fine. The ammo might actually rest centered in the chamber w/respect to the bore.
But concentric ammo could not even chamber in some of my barrels -unless it was also -straight-

When you look at an H&H, think of a jump rope. This concentricity gage sees only displacement of the rope's arc nearest one end(a pinned end). That's fine because it's not a runout gage.
Now look at a Sinclair. You note here that the center of the rope is pinned, and displacemnet of it's arc is indicated at a free end. This won't show the concentricity of the arc. But trust me, if you straighten that rope, it will be concentric.

 

[Boss Hoss]

Mike----the Sinclair is a good unit however I have them both and the H&H works better for me. Very seldom I have to correct ever so slightly the loaded round which I do right before a match (maybe 15 to 30 minutes and use them for foulers) to keep spring back to a min.

The best way to avoid any of this and 99% of my rounds are good is to have your process refined with all of the problem areas removed which starts with a trued sizing press and goes from there.

The only way to measure dead nuts for neck thickness is to use the Micrometers - Mitutoyo ball style micrometer which is one of the first tools Speedy advised me to get.

Buy the best and cry once I say lol...

 

[Moman]

Mikecr, OK I think I understand it a bit better. I had to go back and look at the picture Boss posted and it started to make more sense. What I still don't understand is why you would use a tool such as the H&H? If you moved the indicator to the middle of the case with both ends pinned, I guess that would tell you something. But you said they measure near the bullet tip, which can show concentricity, but what good is that? Wouldn't you just be better off using a true runout guage? Wouldn't a runout guage show both?

 

[Mikecr]

A concentricity gage will not show everything. That's the whole point of it.
Given this, and it's ability to tweek indicated concentricity, it provides very low & consistant readings. I had & used an H&H for while. It's well built and does just what it's designed to do(but not what we need IMO).
This is so much easier than fixing all the problems to get low TIR,, and many reloaders favor easy.
They take shortcuts like weighing brass, instead of actually checking H20 capacity, etc..

On the flip-side a runout gage will not stop reading at concentric. It will continue to show every wiggle in your ammo until you have worked them all out. It can be brutal, so people do silly things like 'halving' TIR to assume pseudo concentricity.
Don't fool yourself. Straight ammo will measure so from every direction.

Anyway, debates about gadgetry always go roundy. But I believe this combination is the best, as it is all you need to cull for best brass, and verify ammo has low runout: