Concentricity - too deep in the weeds?

[DownhillFromHere]

So Sinclair International's Bob Kohl talks about keeping Total Indicated Runout (TIR) under 0.003" here. He says "good" precision ammo should have 0.003" or less TIR.

Ok, so what I'm finding is all my resized (using RCBS Gold Medal Match bushing die and a Sinclair mandrel) Peterson and Starline 6.5CM cases come in as follows, measured on an RCBS gauge with the case supported as shown in the photo:

1. Case body, measured about 1/8" below the shoulder: 0.0000 - 0.0005"
2. Case neck (measured as shown in the photo): 0.0000 - 0.003" - Distribution:
   > 20% <0.001"
   > 40% 0.0015-0.0025"
   > 35% 0.0025- 0.003"
3. Neck brass thickness varies <0.0005"

Pre-resize measurements are all 0.001" or better.

My Question: Given that I just started looking at case neck TIR (#2 above) and I'm getting consistent sub-two-inch groups at 300 yards (many groups of one inch or even better), do I need to get further down in the weeds trying to eliminate case neck runout? I've already made some progress in doing so. I've been working on getting TIR measured on the bullet about 1/6" in front of the case mouth down to 0.000-0.003" and have gotten that down pretty well.

Yes, I realize I'm making it harder to achieve super-duper concentricity by using a Dillon 550, even tricked out as described in articles by 6.5 Guys and others. Again, consistent 1/2-MOA or better accuracy at 300 yards or more - observed on paper, not steel - suggests that my handloads are adequate, but if improving TIR to <0.001-0.002" will make accuracy better/more consistent, I'll work on it.

 

[918v]

Your measurements don’t mean shit without the bullet seated in the neck. The case with .003” neck runout might have zero bullet runout and vice versa.

 

[DownhillFromHere]

Your measurements don’t mean shit without the bullet seated in the neck. The case with .003” neck runout might have zero bullet runout and vice versa.

I agree up to a point. I wanted to see if there's a correlation between TIR measured on the bullet and TIR of the neck.

So I have now seated bullets in the best (<0.001" TIR) and the worst (0.003-0.0035") neck runout. Bottom line is there is some correlation between neck runout and runout of the seated bullet but not as much as I expected.

The main thing I want to see is if there is significant accuracy difference between rounds with <=0.001" TIR and >=0.003" TIR (measured on the bullet) at 300 yards. That's tomorrow. Cloudy calm forecast - negligible wind & mirage.

 

[308pirate]

This topic is full of mental retardation from people who know absolutely nothing about geometric tolerances of form like runout.

To begin with, there is no such thing as "total indicated runout". There is circular runout, total runout, and total indicator reading.

And I haven't even touched on the datums used to measure them.

The reloading community doesn't know what it doesn't know about measuring runout and I don't have time to take them to school.

 

[sierracharlie338]

This topic is full of mental retardation from people who know absolutely nothing about geometric tolerances of form like runout.

To begin with, there is no such thing as "total indicated runout". There is circular runout, total runout, and total indicator reading.

And I haven't even touched on the datums used to measure them.

The reloading community doesn't know what it doesn't know about measuring runout and I don't have time to take them to school.

Not to mention that the majority of people on this site aren’t remotely capable of the accuracy to determine a difference in .001 or .003 runout even if their gun is. I’m no exception to that.

 

[918v]

This topic is full of mental retardation from people who know absolutely nothing about geometric tolerances of form like runout.

To begin with, there is no such thing as "total indicated runout". There is circular runout, total runout, and total indicator reading.

And I haven't even touched on the datums used to measure them.

The reloading community doesn't know what it doesn't know about measuring runout and I don't have time to take them to school.

Then go the fuck away

 

[918v]

I agree up to a point. I wanted to see if there's a correlation between TIR measured on the bullet and TIR of the neck.

So I have now seated bullets in the best (<0.001" TIR) and the worst (0.003-0.0035") neck runout. Bottom line is there is some correlation between neck runout and runout of the seated bullet but not as much as I expected.

The main thing I want to see is if there is significant accuracy difference between rounds with <=0.001" TIR and >=0.003" TIR (measured on the bullet) at 300 yards. That's tomorrow. Cloudy calm forecast - negligible wind & mirage.

Every time you seat a bullet you’ll get a different amount of runout.

Runout is something that doesn’t affect accuracy very much. If you’re within .003” than you’re twice as good as factory match ammo.

 

[DownhillFromHere]

Every time you seat a bullet you’ll get a different amount of runout.

Runout is something that doesn’t affect accuracy very much. If you’re within .003” than you’re twice as good as factory match ammo.

And that's why I asked the question about going too deep in the weeds. It would appear the answer is yes, get out of the weeds.

I'll find out soon enough whether there's an accuracy difference between <=0.001" and >=0.003" with my loads. It's a matter of simple curiosity to me so I posted here to see if it has been to anyone else.

Your comment about factory ammo further stirred the pot so I looked at 5-10 rounds each of factory Hornady 140 ELD-M, 147 ELD-M, and 140 American Gunner. Most of the rounds were 0.002-0.003" with a couple near 0" and a few 0.004=0.005".

 

[clcustom1911]

I'm with @308pirate on this one.... too far in the weeds. If you wanted to find out how to best figure out how this concentricity thing affected your loads, you would need to make loads with 0.000, 0.001, 0.002, 0.003, etc runout, and shoot them with the same orientation (i.e. the side with the most indicated runout chambered at 12 o'clock) Also need to know if your chamber is concentric to your bore, in line with your bore, etc. You would need to shoot a handful of those those runout rounds indexed at 12, 3, 6, 9 o'clock positions because.....

If you have perfectly straight ammo, what good is it if your chamber is .0005-.001 out of alignment, or .01 degrees out of alignment in relation to the bore axis, causing bullets to enter the bore at a cunt-hair off angle anyway?


You know what I do? Load and shoot.

 

[308pirate]

And that's why I asked the question about going too deep in the weeds. It would appear the answer is yes, get out of the weeds.

I'll find out soon enough whether there's an accuracy difference between <=0.001" and >=0.003" with my loads. It's a matter of simple curiosity to me so I posted here to see if it has been to anyone else.

Your comment about factory ammo further stirred the pot so I looked at 5-10 rounds each of factory Hornady 140 ELD-M, 147 ELD-M, and 140 American Gunner. Most of the rounds were 0.002-0.003" with a couple near 0" and a few 0.004=0.005".

Your data is meaningless

 

[chevy_man]

I'd bet anything your rounds will be different if you chamber them from a mag, pull them back out and check again.

I've seen zero difference when I've checked and sorted.

My theory is when you put 50k+ psi behind it the bullet straightens itself in the bore quite quickly and doesn't affect a thing.

 

[Mark1954]

Your data is meaningless

The reloading community doesn't know what it doesn't know about measuring runout and I don't have time to take them to school.

If you don’t have time to share your vast knowledge on the topic, then why don’t you keep your negative comments to yourself.

 

[forrestgump01]

So Sinclair International's Bob Kohl talks about keeping Total Indicated Runout (TIR) under 0.003" here. He says "good" precision ammo should have 0.003" or less TIR.

Ok, so what I'm finding is all my resized (using RCBS Gold Medal Match bushing die and a Sinclair mandrel) Peterson and Starline 6.5CM cases come in as follows, measured on an RCBS gauge with the case supported as shown in the photo:

1. Case body, measured about 1/8" below the shoulder: 0.0000 - 0.0005"
2. Case neck (measured as shown in the photo): 0.0000 - 0.003" - Distribution:
   > 20% <0.001"
   > 40% 0.0015-0.0025"
   > 35% 0.0025- 0.003"
3. Neck brass thickness varies <0.0005"

Pre-resize measurements are all 0.001" or better.

My Question: Given that I just started looking at case neck TIR (#2 above) and I'm getting consistent sub-two-inch groups at 300 yards (many groups of one inch or even better), do I need to get further down in the weeds trying to eliminate case neck runout? I've already made some progress in doing so. I've been working on getting TIR measured on the bullet about 1/6" in front of the case mouth down to 0.000-0.003" and have gotten that down pretty well.

Yes, I realize I'm making it harder to achieve super-duper concentricity by using a Dillon 550, even tricked out as described in articles by 6.5 Guys and others. Again, consistent 1/2-MOA or better accuracy at 300 yards or more - observed on paper, not steel - suggests that my handloads are adequate, but if improving TIR to <0.001-0.002" will make accuracy better/more consistent, I'll work on it.

View attachment 7251327

I might worry about it IF I were shooting benchrest and that's a really big IF . Otherwise I wouldn't worry about it.

Keep in mind that some of that "run out " could be the varience in neck wall thickness if its not turned.

 

[zeroz]

You are pretty deep in the weeds, fairway is over here.

 

[ken226]

 

[Deleted member 113831]

@308 ButtPirate

 

[shoot4fun]

Once upon a time I shot short range Benchrest. Here is my experience gleaned from the sport. This, you all must realize, is MY and only MY experience and others will differ.
The 6PPC is one helluva short-range accuracy producer. Proof? It has been, though many tried other things, been king of that discipline for many years and there is nothing even close to knocking it off that pedestal. I've also learned a lot about rifle accuracy and what it takes to achieve it since (and due to) those days. Once, at a rather large match, another shooter was talking runout as if he were a "runout scholar". He compared his runout from loaded rounds to mine and exclaimed there was no way my ammo (producing from .006-.010 bullet runout) would never "shoot". Still, my loads and equipment let me turn out results that, back in that time, were well into the top of the pile category. Today I still measure bullet runout, but only early in the seating process, to verify things are all in order. It is my opinion that bullet runout is not a four-alarm fire but merely an indicator that I need to "clean up" something in my seating process. My unscientific testing has shown me the largest single contributing factor to runout is what happens as during the initial seating of the bullet and that, especially, a bullet that strike the die body on the way up is going to be lacking the concentricity of the rest.
Bottom line is the reloader should concentrate his/her worrying on other variables instead.

 

[DownhillFromHere]

I appreciate all the constructive comments ("constructive" includes "you're too deep in the weeds," which is part of the title of the thread). My curiosity itch has been scratched.

Earlier this week, I put 10 of my best rounds (0.0000 - 0.0005" runout) and 10 of my worst (0.003 - 0.004") on paper at 200 yards. I would have preferred 300 or more but wind and mirage pushed me back. Anyway, there was no difference. The sample size is small and wind/mirage almost certainly hurt groups... normally I get consistent 1-inch +/- 1/4" at 300 in optimum conditions, and this time I got 1-1.25 inch at 200... but I saw enough on the range and in this thread to set aside "concentricity" as a significant factor in accuracy of my handloads.