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I have been reloading for 40 plus years and have gone down many rabbit holes but not this one. I have always tried to buy good equipment and dies to hopefully minimize run out on my loaded ammo, but until recently, I have not really measured it. I recently bought a sinclair concentricity guage and have found some surprises with my ammo. Some has measured quite good, .004" and under and as good as .0005". Other ammo is all over the map and as bad as .010" plus total run out. I have some new equipment and dies on order to tame my "problem children". My goal is to make my precision hunting and target ammo have .002" or less total run out. Having the tool to test where the run out is induced is the first step towards recovery. What is your experience with concentricity and accuracy, is the juice worth the squeeze? Fire away!
 
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Well, that brings up a good point, and something I've overlooked recently.

When loading 30-06 with my RCBS dies, runout is about .001 to .0015". Since that's basically a reflection on the bullet seating die. I never checked again.
When switching to 30-06 AI and neck sizing only, runout was low just like with "normal" 30-06.
But this year I bought a Redding full length sizer for my AI and haven't checked. Kinda forgot I had the tool to do so.
Good question, @osprey.
 
The bullet seating die will have the biggest effect on this. My go to is the Forster micrometer competition bullet seating die.

You can bend necks which will lead to runout with improper technique using a ball expander if you're not careful. This is also why I use a carbide mandrel to size the inside of the case mouths.

Starting with quality brass is also a big step in the right direction. If the brass is not fairly consistent regarding even neck thickness, it can cause problems with runout and neck tension.
 
To answer your question more directly, RCBS claims runout to be one of the biggest detractors from accuracy.

I have personally seen differences when runout is around .006"-.007" or greater. At the lower end below that, I'm not sure my capabilities can discern a difference.

You can also mark the high spots on rounds with runout and orient them the same way in the chamber. This can sometimes show you a difference on paper, but not always depending on the severity of the runout.
 
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Well I have established a few things so far with regards to concentricity with my .223 reloading.
My redding turret press vs my rcbs rockchucker press is a toss up for making concentric ammo. My .223 rcbs fl sizing die is not totally the culprit for crappy run out, in fact it seemed to improve concentricity of the case after being sized. Rotating the case several times during bullet seating does not help concentricity, in fact it appeared to make it worse. I sized 20 lc cases and all came out within .002" total run out measured half way up neck. Seating was where things went South a bit. Best total run out measured at bullet just above case mouth was just under .001". Worst was just over .006". I suspect as Dizzy alluded to, case neck thickness and how the cases are interacting with the expander has much to do with inconsistent concentricity. More to come on that. For now I will go shoot the 6@ that are .003" and under and compare them to the 6@ that are .004"+ to .006+. This is a known accuracy load so it will be interesting to compare chrono and accuracy data between the two 6 shot groups. Keep the tips coming!
 
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For me one of the ways I cut run out problems was the way I set up my sizing die . I found that the cases that I deprimed as a separate step came out with less run out! And those that I deprimed as I resized always had more run out! What I figured out was if i lifted the sizing ball up high enough that it just cleared the neck on the down stroke, as it started back up the neck was still held in the die and got a good straight start. With it set low enough to deprime the case on the way back up the case neck was in the open body of the die and only held in place by the shell holder. With a case in that position grab the brass and see how much wiggle there is!
This helped me, Good luck, DR
 
I have been depriming with a separate step for 8-10 years now, albeit for different reasons. Good to know it also helps with my quest for less run out.
 
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To answer the original question ... well "it depends".

Gross amounts of run-out will definitely affect accuracy, but smaller ones may not even be noticeable if any number of situations exist. Things like how concentric is your chamber, how consistent is the case wall thickness, how much excess cartridge headspace are you using, the accuracy potential of the bullet chosen ... etc. All of these (and more) can cause more problems with accuracy than bullet run-out.

So, what type of rifle are you shooting? What type of ammo are you loading? What are the ultimate goals for the combo?

So as an example, for me at least, I couldn't care less about runout in my "run-n-gun" battle AR loads, if they chamber I'm happy as I'm just trying to make a huge silhouette go "ding" inside a couple of hundred yards.

On match rifles that I shoot out to 600 yards (and occasionally longer) or my .220 Swift varmint gun (that I don't even think of using until the ranges go out to 300 yards or so) run-out becomes one of the things I take the time to address.

Hope this helps.
 
I am starting with my 223 ammo loaded for a 20"precision AR I put together in 223 wylde. It has a WC super sniper barrel with 1-8 twist. In my limited testing it has shown great accuracy potential with 60gr Nosler ballistic tips. I pretty much try to bump all my shoulders back .002 - 003" so headspace is not excessive. This rifle will be used for varminting from a bench or a stand and out to 600 yds or so for informal bench shooting. I guess my goal is to first identify how much run out is acceptable before accuracy is degraded. With that info I would like to tighten up my run out #s to an acceptable level for this rifle. Beyond that I will go down the same path with my big game bolt rifles in 6.5 cm, .270 win and 280ai. Overall I hope what I learn trickles down to all my loading to make more consistent ammo.
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I started playing around with my 270 win forster fl sizing die last night. It is supposed to be one of the best fl sizing dies for maintaining concentricity by virtue of the expander button orientation. Despite being adjusted correctly and good inside neck lube, mine is definitely inducing some runout to fire formed case. Anybody use a body die to size body and bump shoulder and a mandrel or lee collet die for sizing neck? That is the path I am going down next as new dies should be here later this week.
 
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You're eliminating one more variable when you minimize runout.
Part of runout, and one that few measure, is how square the base of the cartridge is to the axis of the cartridge, and the accuracy of this measurement really depends on the design of your concentricity gauge and how accurately you mount the cartridge.
That said, if your bolt face is not square, you're forked anyway, as the base of the cartridge will deform to the bolt face angle.
 
You're eliminating one more variable when you minimize runout.
Part of runout, and one that few measure, is how square the base of the cartridge is to the axis of the cartridge, and the accuracy of this measurement really depends on the design of your concentricity gauge and how accurately you mount the cartridge.
That said, if your bolt face is not square, you're forked anyway, as the base of the cartridge will deform to the bolt face angle.
Post firing examination of brass before reprocessing is a very important step. I track weight and growth per casing for my precision rifle. But there are also not thousands of them.
 
The rifles I am using are all known quantities that have shown good accuracy and have no known defects. Fireformed cases measure out great showing no excessive headspace or bolt face anomalies. The concentricity tool I am using is the sinclair.
 
About six months ago I ordered some redding type s fl bushing dies for my bolties in 6.5 cm and 280 ai. What I found is the induced more runout than my regular redding fl dies. Like twice as much. Still I like the idea of not dragging that expander ball through the cases so after some research I stumbled on to some aftermarket bushings made by short action customs. They are made with a lead in that is slightly tapered to help guide neck into bushing smoothly aiding in keeping it concentric. Today it showed up in the mail and I went right out to my reloading room and sized 5 cases with it and I'll be dipped if it didn't do just as advertised. The 5 cases I sized showed an average of .0005" of run out. That compares to an average of .003" before with the redding bushings. I will take take that improvement every day! We will see what happens when I seat some bullets in them with a new die that is due tomorrow along with some other goodies.
 
Well more goodies came today and good progress was made. I seated the 6.5 CM bullets on top the case that got resized with the redding S bushing die with the short action custom bushing. I used the new Mec Marksman press that came in the mail along with a new redding competition seating die. Total average run out was barely over .001"measured at bullet. I then moved to 270 win and used a redding body die to size 20 cases followed up with a Lee collet neck die to squeeze the necks down to size.This also yielded fantastically concentric brass. I then seated the bullets with a forster seating die on the Mec and run out measured at bullet averaged about the same as using the process employed on the creedmoor ammo. I guess for streamlining a step the S die routine is a bit quicker but both yielded great results and neither of these cartridges are high volume so it doesn't really matter in the end. Although I can't really say the Mec marksman's floating shell holder design really helps concentricity that much, it seems to be a solid press with smooth action. I will try to get to the range this weekend and see if any of this improvement in my process shows up on the target.
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