Bullet concentricity - what is the most meaningful measurement?

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jepp2

New member
I want to improve the concentricity of my future rifle loads.

I had access to a Redding and a Hornady tool and measured some of my previous loads.

I realize the Redding measures relative to the case body. Most of my loads were running about .005-.007" T.I.R.

The same loads when checked on the Hornady tool were run-out is relative the cartridge base. These measured .001-.002" T.I.R.

So I am just trying to hear from others what you find as the most useful measurement basis? It all might come out in the wash in the future as I reduce my neck run-out and improve the bullet seating.
 
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Jimro

New member
Runout is something to worry about if and only if you are chasing "one ragged hole" in the paper.

Jimro
 
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dahermit

New member
Once a cartridge is fired, the head of the case is no longer concentric with the rest of the case. I will not go into why. That is why most concentricy gaging is done with the body of the case. The bullet run-out should be as little as possible for accurate ammunition. Old NRA article revealed that .002 or less should be the standard for target quality rounds.
Also, despite some tools that are intended to straighten rounds out of that range, it is a waste of time, asmuchas once the bullet is straigtened, it still did not shoot accurateley.
 
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jepp2

New member
dahermit, exactly the information I was looking for, thanks!

I have been working to improve the neck runout as measured relative to the body reference (via the Redding tool). As others have found the Lee collet dies are much better than other means. Next I am focusing on bullet seating.

And of course I am both seeking the single ragged hole on some rifles, and just consistent groups on others.
 
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wncchester

New member
Understand that if the case neck itself is bad (bent or non-concentric) no sizer or seater will be able to make straight ammo with it. Skim turning the necks, just enough to clean up maybe 75% of the exterior, helps but a lot of people over turn necks and that makes an already sloppy fit worse.

Lee's neck sizer will make the straightest possible necks AND make the inside diameter the largest possible for straight seating. Most folk seem to think a "high tension" neck is great but it isn't; all the extra seating force does is expand the neck to about what the Lee Collet does and the excessive seating resistance tends to force bullets to start crooked. Once a bulllet starts crooked it's virtually impossible to completely straighten it out.
 
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dahermit

New member
I had an interest in concentric at one time and got some interesting results from measurements. I tested the concentric of an unfired factory round and found that it was perfect, that is .000 on the bullet run out. I then fired the cartridge and put the empty fired case in the gage and measured the neck for concentric and found that it was .000 also...showing that the rifle chamber's neck was concentric with the chamber body. In other words, any lack of concentric in the rifle was not the cause of the rifle.
I then sized the case in an RCBS full-length sizer with the die backed out to only neck-size. The resultant sized cases measured from .002 to about .006, showing that out of concentric was caused by the sizing process. To sum, the cartridge cases go into the rifle chamber concentric, the cases come out still concentric, it is when the cases are sized that things get out of whack. I had an RCBS die that usually produced loaded rounds .017 out of concentric with the cartridge body. Switched to a Redding die, got better results. That was before Lee Colet Dies. Have a .308 Win. Lee Colet Die that will produce about 50% output at .002 or less...I pull the bullets on the others and resize. I should probably spend some time turning the cases to about 75% of total clean-up, but do not shoot rifle much anymore to keep experimenting.
 
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dahermit

New member
If you neck size the case, the body is going to determine how it sits in the chamber.
Click to expand...
Exactly. That is why one does not want to push the neck of the case off-center when sizing...and a lot of dies do, or end up doing because the neck wall is thicker on one side than the other.
 
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g.willikers

New member
Aha, and Eureka.
Thanks dahermit.
Now it's clear why my rifle reloading attempts turned out less than stellar.
No where as good for accuracy as factory loads.
Glad I quit trying before leaving a good rifle in the range trash can.
 
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