Concentricity .. how important?

BigSwede

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Canadian border /northern ny
Educate me as to the importance of bullet/brass concentricity. I have experienced great accuracy when I take the time to run every round through the gauge and shoot the groups from the rounds that are "round". Let me hear what you're doing to ensure concentricity.
-Swede
 

J E Custom

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Educate me as to the importance of bullet/brass concentricity. I have experienced great accuracy when I take the time to run every round through the gauge and shoot the groups from the rounds that are "round". Let me hear what you're doing to ensure concentricity.
-Swede

It's been a while since i did a concentricity test but I will try to remember the results as best i can.

I loaded 40 rounds with the same components and shot them in the same rifle. This load was my accuracy load for my 7/08 that will consistently shoot 1/10 tenth moa groups.

After loading, I measured all rounds for concentricity and sorted in this order.
Zero runout.
.001 thousandths.
.002 thousandths.
.003 thousandths
.004 thousandths
and over .004.

All rounds over .004 were straightened and sorted in this order
Zero runout.
.001 thousandths
None of the straightened cartridges were over .001 after straightening.

Obviously, the zero runout as loaded were the best.
.001 to .002 showded very little accuracy loss over the zero runout loads @ 100 yards. 200 yards you "could" see a slight difference
The greater the runout the worse the accuracy.

During this test it became obvious that any ammo loaded with greater than .003 thousandths of runout was unexceptable for someone that strived for accuracy.

Oddly, any load that had been straightened, even though they had zero runout did not shoot as well as those loaded with zero runout. and the ones with greater than zero runout shot about as good as the .003+loaded ones.

So I came to the conclusion that the more concentric your ammo is the more accuracy you will have. The chamber, the bullets and cartridges/ammo shoots best if it is concentric to the barrel bore.
depending on the shooters skills, concentricity may not be a factor at 1 to 200 yards but beyond that It does make a difference.

J E CUSTOM
 

lancetkenyon

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Arizona
Just a question JE, would you say that over 200, like 500-1000+, errors also show up from shooter induced inconsistencies and environmental effects far greater than at 100-200 as well?

Case in point:

.280 AI as seen above @ 100 (.169") .162MOA


Same rifle, same load @ 921 (2.9") .255MOA (if my math is correct?)


Pretty much as accurate as I could hold with a 3-15x Premier in a sub-9# rifle, and was as consistent as I could be that day. To say I was happy would be an understatement. But, chasing that extra .1 is always something I am looking for.

How much do you think run out played in this? I cannot tell you what run out was, as I just grabbed 3 rounds from my hunting loads, which I don't check.
 

J E Custom

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Location
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Just a question JE, would you say that over 200, like 500-1000+, errors also show up from shooter induced inconsistencies and environmental effects far greater than at 100-200 as well?

Case in point:

.280 AI as seen above @ 100 (.169") .162MOA


Same rifle, same load @ 921 (2.9") .255MOA (if my math is correct?)


Pretty much as accurate as I could hold with a 3-15x Premier in a sub-9# rifle, and was as consistent as I could be that day. To say I was happy would be an understatement. But, chasing that extra .1 is always something I am looking for.

How much do you think run out played in this? I cannot tell you what run out was, as I just grabbed 3 rounds from my hunting loads, which I don't check.


No doubt the shooter has a major role in the accuracy and especially at longer distance. This is the reason I held my test ranges to 200 yards.
I also fired the test from a bench type rest to eliminate as much human error. Conditions were very good and all test were fired by me to prevent any differences in shooter skills.

This was just a test to satisfy the concern about the quality of my loads, and loading equipment. All groups were measured with a vernier
4 times and the highest/largest group was used to show the worst case scenario. I have sense, changed my loading procedure to improve the concentricity of the cartridges because I felt it was important enough based on the test to do so.

I also concluded that straightening cartridges could only "Save" poorly loaded ammo, but loading it concentric in the first place was the best.
The concentricity gauge/tool I bought was for checking and straightening. Now I devote more time to loading concentric ammo and keeping an eye on the process and not relying on the tool to fix my sloppiness.

Like everything else In this game, every improvement makes a difference no matter how small the improvement Because we shoot farther than most other hunters/shooters and can use every bit of help we can get. (At least I do).

PS: I prefer to measure group size by flattening out the group on a piece of poster board, then measuring the mark that the bullet made on the edge of the hole.(You can check you measuring prowess by shooting one hole and when measuring correctly, you will get bullet diameter). When measuring a group, I follow the same procedure and find the greatest distance across the group, then subtract one bullet diameter. This will give you an exact center to center group size.
This is the way benchrest groups were measured. even though often i am only a few thousandths different, I log the biggest group size.

Just My Opinion

J E CUSTOM
 

CA48

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Nov 18, 2009
Messages
1,075
Location
Texas
It's been a while since i did a concentricity test but I will try to remember the results as best i can.

I loaded 40 rounds with the same components and shot them in the same rifle. This load was my accuracy load for my 7/08 that will consistently shoot 1/10 tenth moa groups.

After loading, I measured all rounds for concentricity and sorted in this order.
Zero runout.
.001 thousandths.
.002 thousandths.
.003 thousandths
.004 thousandths
and over .004.

All rounds over .004 were straightened and sorted in this order
Zero runout.
.001 thousandths
None of the straightened cartridges were over .001 after straightening.

Obviously, the zero runout as loaded were the best.
.001 to .002 showded very little accuracy loss over the zero runout loads @ 100 yards. 200 yards you "could" see a slight difference
The greater the runout the worse the accuracy.

During this test it became obvious that any ammo loaded with greater than .003 thousandths of runout was unexceptable for someone that strived for accuracy.

Oddly, any load that had been straightened, even though they had zero runout did not shoot as well as those loaded with zero runout. and the ones with greater than zero runout shot about as good as the .003+loaded ones.

So I came to the conclusion that the more concentric your ammo is the more accuracy you will have. The chamber, the bullets and cartridges/ammo shoots best if it is concentric to the barrel bore.
depending on the shooters skills, concentricity may not be a factor at 1 to 200 yards but beyond that It does make a difference.

J E CUSTOM

JE, are you using the Hornady tool to measure runout and straighten rounds?
 

BigSwede

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Canadian border /northern ny
I am certain that straight ammo shoots better. Now how do you get it straight dead center for your chamber. When I pull fired rounds out of the chamber and check neck concentricity they are much straighter than after I pull them out of the resizing die. Without buying a bunch of dies to find the one that works what should I do. I assume the ideal would be to use the exact same reamer to make your own dies. How can I get the fired brass to stay straight assuming I have Sammi/factory/no turn chambers ??
 

J E Custom

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Location
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JE, are you using the Hornady tool to measure runout and straighten rounds?

That is what I started with because it had the ability to straighten cartridges Including factory loads.

When I switched my priorities to loading better ammo and checking chambers using fired cases, I purchased the Sinclair concentricity gauge. I bought one without the dial indicator they furnished and supplied my on that reads in .0001 to be more precise. It allows me to do more checking for any run out but is not designed to straighten cartridges.

I really like checking fired cases for chamber concentricity with it. But I still have both and sometimes try to salvage loaded factory ammo that is not concentric using the Hornady Lock N Load. The Sinclair gauge also works great for checking new cases for runout.

J E CUSTOM
 
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J E Custom

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Messages
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Location
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I am certain that straight ammo shoots better. Now how do you get it straight dead center for your chamber. When I pull fired rounds out of the chamber and check neck concentricity they are much straighter than after I pull them out of the resizing die. Without buying a bunch of dies to find the one that works what should I do. I assume the ideal would be to use the exact same reamer to make your own dies. How can I get the fired brass to stay straight assuming I have Sammi/factory/no turn chambers ??

Normally it is not the dies that cause the cases to be formed off center, It is the press. Any misalignment in the press with the dies may cause the misforming of them. What seems to help starts with turning all of the necks true and equal in thickness, Then if the chamber is truly concentric, it will produce concentric cases. Next it is important to allow the shell holder/shell plate the ability to self align with the dies, Some presses also have a floating die holder to also help align cases in the dies. I am currently in the process of buying a press with these features.

The other thing one can do is as he/she is loading, check the concentricity as they go through the process. One thing we used to do to help was halfway through the bullet seating process we stopped and rotated the loaded case 1/2 turn and finished seating the bullet.

Checking with a good concentricity gauge will normally show if you have poor equipment and/or a poor procedure.

J E CUSTOM
 
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Reloader222

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Jun 4, 2010
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251
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South Africa Limpopo
Up to 0.002" is still good for hunting. When you punch papers less than 0.002" is preferred.

When checking the run out, mark the all case with a pen at 12 o'clock and sort them in groups. When loading them in the magazine, you load the cartridges with this marking to the top. By doing this you will get ever tighter groupings since the run out is pointing in the same direction.
 

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