At what point does cartridge runout erode accuracy?

[Mulligan]

This may not be the answer that most people want to hear, but I’ve always wondered the same thing so this year I did something about it. I loaded up 350 rounds of 6 dasher identically and after I was done I measured each and every one of them using the 21st century concentricity gauge. I selected the worst 150 rounds for bullet TIR, 5mm in front the tip of the bullet. They ranged from 0.0035” to 0.006”.
I brought them to a two day 1000 yard F Class Open competition and truly expected to score horribly. My personal best at 1000 yards is 973-34X. The weather, both days, was very similar to other times I had shot at 1000 yards at this range. I ended up shooting 966-30X. That’s less than 0.7% reduction. Not that significant. However, in all fairness; I feel like I could better answer the question if I had shot the 150 rounds that measured the best for a true comparison.
Dave

How does the 966 compare to your average?
CW

 

[Phys86]

At some point it will matter, but 2-4thou is not the end of the world unless your chamber is tighter.
I wouldn't stress out over it.
But there is an opportunity here to learn. What is causing the issue? Just figure it out and fix it.

What do you mean exactly by tighter chamber? Through the body, or neck, or both?

 

[garandman]

If the Hornady gauge can be trusted, I'm getting less than 0.001 runout, and also getting 0.2 - 0.4 moa at 100 yard. Cause and effect? Who knows. But I'm not enuf of a nerd to try increasing amounts of runout and test for degrading accuracy.

I guess in theory, if the bullet is so far out of concentricity that one part of the ogive hits the lands before another part of the ogive, the bullet could possibly fly wobbly due to the lands marks. Maybe. Possibly.

 

[BoydAllen]

I have an H&H concentricity gauge that is designed to facilitate straightening. It incorporates a toggle for that purpose. I have generally seated bullets into the lands for my 6PPC. Once out of curiosity I used the straightening feature to bend a round so that it had .0035 TID instead of the usual less than .002. I chambered the round and then removed it. (The rifle does not have an ejector.)and then measured its runout, which was .0015. I came to the conclusion that with thin necks, (.0085 at the time) shallow neck engagement ( less than .140) and bullets that have pressure rings, all of those factors combine to make somewhat flexible joint so that forcing the bullet into the rifling straightens the round. Years back I was told that you will not see any on target effect of runout at .002 or less. For longer bullets with long ogives and boat tails I am not sure that this would be the same.

 

[garandman]

I came to the conclusion that with thin necks, (.0085 at the time) shallow neck engagement ( less than .140) and bullets that have pressure rings, all of those factors combine to make somewhat flexible joint so that forcing the bullet into the rifling straightens the round.

Did you see any effects on your target of the rifle chamber straightening the round?

 

[BoydAllen]

Did you see any effects on your target of the rifle chamber straightening the round?

I did not do that test. I probablyu used the round to foul the bore. I will tell you one thing that may relate, and is why I didn't bother testing it. I have found that if a case is dropped onto a hard floor, denting the neck, even though you round it out and then resize it so that it looks perfect, it will produce a filer for the next firing. After that it will shoot OK. While this is not directly related to a round where the bullet was forced out of alignment , it tends to make me not use rounds that have been treated differently in a group.

 

[Steve Blair]

The late Don Nagel once said, "There's about twenty things I do when reloading. I think only about ten are necessary, but I don't know which ten."

 

[Larry Koch]

Really you have to define accuracy.
Some folks like to shoot the same hole 5 times.
Some folks are happy hitting the paper plate at a 100 yards

If you can roll your cartrige on smooth flat surface and the tip of the bullet does not move at all.
I would say its good enough for hunting. And target shooting.
But in competetion take nothing for chance.

 

[garandman]

The late Don Nagel once said, "There's about twenty things I do when reloading. I think only about ten are necessary, but I don't know which ten."

Prolly the best summary stmt I've heard about reloading.

 

[Stan Taylor]

Prolly the best summary stmt I've heard about reloading.

The late Don Nagel and I shot 1000yd benchrest together when he wasn’t shooting F-class made a lot of barrels for him an totally miss him he was very dedicated to the sport.

 

[Steve Blair]

The late Don Nagel and I shot 1000yd benchrest together when he wasn’t shooting F-class made a lot of barrels for him an totally miss him he was very dedicated to the sport.

Don was a good man and was recalled much sooner than expected.

 

[Stan Taylor]

Don was a good man and was recalled much sooner than expected.

Ain’t no doubt he and I have worked on a lot of projects over the years i used to love the sayings Don would say at the matches looking at my targets and say your waterline is good .

 

[MikeWhy]

... selected the worst 150 rounds for bullet TIR, 5mm in front the tip of the bullet.

For consistency's sake, maybe TIR should be measured at CBTO rather than at the tip?

(Just stirring the pot. Do carry on. I'm learning a lot.)

 

[Hondo64d]

I have searched the web, cannot find a good study or really any solid information on the relationship between straight ammo and accuracy.
Is there a correlation between small groups and really straight ammo?
Does building concentric ammo help with accuracy? If so, how much matters?
CW

I think it was Jon Barsness that did an article years ago that included results from shooting more concentric rounds vs less concentric. Now I’m pulling this from memory and it’s been a while, but if I recall correctly, in a hunting weight rifle with a top notch barrel, he could not detect an adverse affect on groups until runout exceeded .005”. In a benchrest rifle, that number was smaller, maybe .002”, but I can’t remember for certain.

I just try to get my ammo as straight as I can without sorting cases or turning necks. With my current setup, that is about .001 - .002”.

John

 

[JFrank]

I gave up on chasing consentricity, I couldn't shoot the difference from one to another.
To coin a phrase " there are bigger knobs to turn"

 

[garandman]

For consistencies sake, maybe TIR should be measured at CBTO rather than at the tip?

(Just stirring the pot. Do carry on. I'm learning a lot.)

Thats how I do it....



Well...technically, I stopped measuring conccentricity when I started using chamber type seater dies from LE WIlson. They make it basically impossible to NOT be concentric. That way, if it *is* an issue, I've already eliminated it.

 

[mikecr]

What do you mean exactly by tighter chamber? Through the body, or neck, or both?

Anywhere a chambered banana can bind.
Upper body, shoulder, neck, bullet.

If your loaded ammo measures 2thou of TIR at body-shoulder junction for example, and if this puts a case in interference with your chamber, then that is a pressure point that is likely less than consistent.
A high number of FL sizing cycles could put you there.
If you make dead straight cases, but your seating causes 3thou TIR at exposed bullet bearing, then you'll likely force interference with freebore. The case may not be able to lie angled enough in a tighter clearance situation to relieve pressure at that freebore.

But your reloading has to be really bad to cause all this.
And maybe you'd embrace the 'rat turd in a violin case' relief, as it must seem easier than good reloading.
It's just way different from my view of things.

 

[Phys86]

Anywhere a chambered banana can bind.
Upper body, shoulder, neck, bullet.

If your loaded ammo measures 2thou of TIR at body-shoulder junction for example, and if this puts a case in interference with your chamber, then that is a pressure point that is likely less than consistent.
A high number of FL sizing cycles could put you there.
If you make dead straight cases, but your seating causes 3thou TIR at exposed bullet bearing, then you'll likely force interference with freebore. The case may not be able to lie angled enough in a tighter clearance situation to relieve pressure at that freebore.

But your reloading has to be really bad to cause all this.
And maybe you'd embrace the 'rat turd in a violin case' relief, as it must seem easier than good reloading.
It's just way different from my view of things.

I like those answers

 

[Ned Ludd]

For consistency's sake, maybe TIR should be measured at CBTO rather than at the tip?

(Just stirring the pot. Do carry on. I'm learning a lot.)

^^^This. The axis/angle of a bullet that is not perfectly concentric to the neck walls remains constant. The longer the bullet, the greater the indicated runout at the tip.

As to how much TIR there can actually be before precision is affected, that's a more difficult question to answer definitively. A while back, I purchased a pet chimp to be my BFF and to help me reload ammo. I named him Cocopuff. Cocopuff is a very quick learner and it didn't take him long at all to "master" the reloading process. Illustrated below are a few rounds he loaded for me for a recent F-Class match. It's probably fair to state that some of those rounds might have a little too much TIR. Cocopuff still has more to learn about minimizing runout, and maybe just needs to pick up a teeny bit more finesse determining CBTO for loaded rounds using the caliper, but I'm sure in no time at all he'll loading up match-winning ammo for me.

The moral to this story is that if the ammo looks it was loaded by a well-trained chimp, it might have too much runout.

 

[Dave M.]

How does the 966 compare to your average?

The average 1000 yard two day competition score I’ve posted over the last 4 years is 959.
So honestly, about the same relatively speaking. 7 points is a tiny amount over 5 rounds.