I got theHornady on a whim. Not sure why... I don't like most of what else they make....
At what point does cartridge runout erode accuracy?
- Thread starter Mulligan
- Start date
Dave M.
F-Open Class shooter (284 win, 6dasher, 6.5-7PRCW)
Lol. Neither do I but I still find myself loading on a 20+ yr old hornady single stage press that makes some pretty damn consistent ammo.I got theHornady on a whim. Not sure why... I don't like most of what else they make....
jackieschmidt
Gold $$ Contributor
I have actually one test on this subject with my Rail Gun chambered in 6PPC.
Several years ago, BRUNO came out with a little loaded round checker/straightener. The late Gene Bukys and I spent the better part of the day deliberately inducing as much as .005 runout in rounds to answer the question. Keep in mind, my rail with the barrel and bullets I was shooting was capable of putting 10 shots in less than .200 at 100 yards.
Our conclusions were that up to .005, it made no difference. We did not go over .005 because it was difficult to induce that much run out without compromising neck tension. My dies pretty much produce rounds with no more than .002 runout. I have also fcome to the conclusion that most runout is induced in the sizing operation.
Several years ago, BRUNO came out with a little loaded round checker/straightener. The late Gene Bukys and I spent the better part of the day deliberately inducing as much as .005 runout in rounds to answer the question. Keep in mind, my rail with the barrel and bullets I was shooting was capable of putting 10 shots in less than .200 at 100 yards.
Our conclusions were that up to .005, it made no difference. We did not go over .005 because it was difficult to induce that much run out without compromising neck tension. My dies pretty much produce rounds with no more than .002 runout. I have also fcome to the conclusion that most runout is induced in the sizing operation.
The only way you can see straight ammo, and full TIR, is with a v-block type runout gauge.
Your numbers with the Hornady neck bender are way lower than actual.
Your brain resists this, I'm sure, but think about it:
When you pin both ends of the round, you've setup a jump rope scenario.
If you wanted to see the full arc of that jump rope, would you indicate near one of it's ends?
No, you would have to measure in the center of arc.
That's not what you're doing.
With a v-block you pin the casehead and body, moving the arc to the bullet tip.
Then you're measuring near that full arc, seeing TIR.
And none of this was ever about eccentricity (misnomer'd as concentricity).
It's about making STRAIGHT ammo (not centered ammo).
If concerned about that just remember that straight ammo is also concentric, while concentric ammo can present any amount of runout (it can literally be any shape).
You can 'center' a warped 2x4 on a lathe, right? And you don't want to be chambering warped 2x4s right?
You want dead straight 2x4s to begin.
Your numbers with the Hornady neck bender are way lower than actual.
Your brain resists this, I'm sure, but think about it:
When you pin both ends of the round, you've setup a jump rope scenario.
If you wanted to see the full arc of that jump rope, would you indicate near one of it's ends?
No, you would have to measure in the center of arc.
That's not what you're doing.
With a v-block you pin the casehead and body, moving the arc to the bullet tip.
Then you're measuring near that full arc, seeing TIR.
And none of this was ever about eccentricity (misnomer'd as concentricity).
It's about making STRAIGHT ammo (not centered ammo).
If concerned about that just remember that straight ammo is also concentric, while concentric ammo can present any amount of runout (it can literally be any shape).
You can 'center' a warped 2x4 on a lathe, right? And you don't want to be chambering warped 2x4s right?
You want dead straight 2x4s to begin.
Bench rest is less susceptible to bullet tilt, because the tight chamber bends the cartridge straighter.
a) Concentric ammo is a recurring task.
b) Concentric chambering rifles is a one time task.
Human nature is to work harder on non recurring.... which is a mistake..... sorry gunsmiths.
--------------------------------------------------------------------
I had to get the copy machine to scan and covert to text.
-----------------------------------------------------------------------
from "The American Rifleman" ~ 60 years ago, and the NRA says it is ok to quote.
"Gauging Bullet Tilt"
THE MOST PRECISE AMMUNITION
FROM A LOT CAN BE SELECTED
WITH A BULLET ALIGNMENT GAUGE.
By A. A. ABBATIELLO
Other factors being normal, bullet
tilt with respect to the case center-
line affects group size. If the barrel
length and twist are known, it has been
found possible to predict the direction
from the group center in which the tilted
bullet will strike. If the amount of tilt
is known, the distance from the group
center can be predicted.
Significant score improvement has
been noted by those who have tried
such gauged ammunition.
In cal. .30 long-range shooting, the
best match-grade ammunition will group
in one to 2 minutes of angle under test
conditions. Part of this spread is due
to the bullet tilt with respect to the
case centerline, imposed by the bullet-
seating tool. This tilt displaces the bul-
let’s center of gravity slightly to one
side; in bullets such as the cal. .30 Ml,
the amount is about 1/8 the displace-
ment of the bullet point. It enlarges
groups by amounts up to one minute.
These deviations become proportion-
ately less as the tilt is reduced. Tilts
over .O04" do not seem to increase the
dispersion of the group beyond the ex-
pected one minute. Perhaps this is
because a well-fitting chamber has a
tendency to straighten any rounds
which are excessively tilted. Other ex-
planations are possible.
The gauge consists of a V-block
which permits rotating the round about
the bullet point and 2 tangent spots
near the case head. A dial indicator
which reads in tenths of thousandths of
an inch (.0OO1") bears on the bullet
near the case neck. Half the total indica-
tor reading is used as the displacement
for determining the classes into which
the rounds are separated. The high point
is also marked at this time for orienta-
tion of the round in the rifle chamber.
Rounds with .0O2" tilt or less can
be considered good enough for long-
range use, while those with .O03" and
.OO4" tilt are best used only at short
ranges. In general, it was concluded
from target results that each .0Ol" of
tilt will increase the group spread about
1/4 minute of angle, up to a maximum
of .OO4" as mentioned above.
Under test conditions, it was found
that when the rounds were chambered
with the high point always in the same
orientation, the groups were smaller
than when it was randomly oriented.
Gauging and orienting the rounds can
produce the smallest groups of which
that ammunition is capable.
These ammunition refinements are
becoming important, particularly in
long-range matches.
The essentials of the tilted bullet were
discussed in detail no less than 50 years
ago by Dr. F. W. Mann in his book
"The Bullets In Flight". He pointed out that
the balance of the bullet and the spiral
path of the center of gravity are of
high importance in accuracy.
Following a discussion between
George L. Jacobsen of Frankford Arse-
al and the writer at the 1959 National
matches, a trial of the effect of neck
concentricity was carried out by Jacob-
sen. He described his results in ".30-’O6
Cartridge Cases And Accuracy", which
appeared in THE AMERICAN RIFLEMAN,
January 1960, page 20.
SEATING TOOL A FACTOR
The effects which Jacobsen found,
though small, are essentially in agree-
ment with the work reported here.
However, he did not separate the effects
of neck eccentricity and the bullet cen-
ter-of-gravity location with respect to
the bore. The angular direction of the
bullet seating tool is a controlling factor
in the initial position given to the bullet,
rather than merely case neck eccen-
tricity. Case necks can be centered or
eccentric, and the bullet can be inclined
in completely random directions. The
tilted bullet is believed to be the main
cause for center—of-gravity side shift.
The cal. .30 boattail bullet of 173 grs.
weight was selected for these tests be-
cause it is in common use and is of
sufficiently high quality for use in the
National Matches.
Using the gauge shown, 42 ammuni-
tion lots were sampled and the high
point was marked on each round gauged.
These rounds were grouped in steps of
.OO1" bullet tilt, and the data tabu-
lated. The results gave a bell—shaped
curve for 829 rounds of match ammu-
nition, peaking at about .0O2" (see
illustration). Measurements on Service
ball ammunition produced a curve of
similar shape, but peaking at about
.0025" tilt.
This graphically illustrates that even
match-grade ammunition has appreci-
able variations. There is a large spread
among particular lots and boxes. In
general, 10% to 20% of each lot, de-
pending on ammunition quality, falls
into .0O3", .0O4" or even up to .O10"
tilt. Run-of-the-mill ammunition can
thereby enlarge groups to about twice
the size which the same ammunition
can show when it is gauged before firing.
Since the tilt angle of the bullet is
so small (about 1/4 °) it is difficult to
perceive visually. The gauge, however,
makes the sorting a fast, routine step.
A mathematical solution of this prob-
lem was also tried (see box) and is in
good agreement with the results ob-
tained. It is gratifying to find the math-
ematical solution and the experimental
results in agreement.
MATHEMATICAL SOLUTION
A laterally displaced center of
gravity moves through the rifle bore
in a helical (screw) path. The pitch
of this helix is the pitch of rifling,
and its radius is the lateral displace-
ment of the center of gravity. On
leaving the muzzle, the center of
gravity continues in the direction it
had at that point. For example, if it
leaves at top of the bore and rifling
is to the right, the departure will be
to the right. The bullet travels ap-
proximately 2l.5" in a 24" barrel,
making 2.15 turns in the 10" twist
of rifling. The number of turns
shows the orientation on emergence
compared with that in the chamber
before firing. The angle of emer-
gence is that angle whose tangent is
2 pi times the lateral displacement
divided by the rifling pitch. For
.004" point displacement and I0"
rifling pitch, the tangent is 1/8(2·pi)
(.004)/l0 and the corresponding
angle is 1.1 minutes.
The displacement on target from
this cause is proportional to the
range and can be obtained without
noting the angle. For example, ,004"
point displacement gives in l0"
rifling pitch, so far as this mecha-
nism goes, a target displacement at
100 yds. (3600") indicated by the
proportion .00l· pi /10=X/3600, from
which x =1.1".
a) Concentric ammo is a recurring task.
b) Concentric chambering rifles is a one time task.
Human nature is to work harder on non recurring.... which is a mistake..... sorry gunsmiths.
--------------------------------------------------------------------
I had to get the copy machine to scan and covert to text.
-----------------------------------------------------------------------
from "The American Rifleman" ~ 60 years ago, and the NRA says it is ok to quote.
"Gauging Bullet Tilt"
THE MOST PRECISE AMMUNITION
FROM A LOT CAN BE SELECTED
WITH A BULLET ALIGNMENT GAUGE.
By A. A. ABBATIELLO
Other factors being normal, bullet
tilt with respect to the case center-
line affects group size. If the barrel
length and twist are known, it has been
found possible to predict the direction
from the group center in which the tilted
bullet will strike. If the amount of tilt
is known, the distance from the group
center can be predicted.
Significant score improvement has
been noted by those who have tried
such gauged ammunition.
In cal. .30 long-range shooting, the
best match-grade ammunition will group
in one to 2 minutes of angle under test
conditions. Part of this spread is due
to the bullet tilt with respect to the
case centerline, imposed by the bullet-
seating tool. This tilt displaces the bul-
let’s center of gravity slightly to one
side; in bullets such as the cal. .30 Ml,
the amount is about 1/8 the displace-
ment of the bullet point. It enlarges
groups by amounts up to one minute.
These deviations become proportion-
ately less as the tilt is reduced. Tilts
over .O04" do not seem to increase the
dispersion of the group beyond the ex-
pected one minute. Perhaps this is
because a well-fitting chamber has a
tendency to straighten any rounds
which are excessively tilted. Other ex-
planations are possible.
The gauge consists of a V-block
which permits rotating the round about
the bullet point and 2 tangent spots
near the case head. A dial indicator
which reads in tenths of thousandths of
an inch (.0OO1") bears on the bullet
near the case neck. Half the total indica-
tor reading is used as the displacement
for determining the classes into which
the rounds are separated. The high point
is also marked at this time for orienta-
tion of the round in the rifle chamber.
Rounds with .0O2" tilt or less can
be considered good enough for long-
range use, while those with .O03" and
.OO4" tilt are best used only at short
ranges. In general, it was concluded
from target results that each .0Ol" of
tilt will increase the group spread about
1/4 minute of angle, up to a maximum
of .OO4" as mentioned above.
Under test conditions, it was found
that when the rounds were chambered
with the high point always in the same
orientation, the groups were smaller
than when it was randomly oriented.
Gauging and orienting the rounds can
produce the smallest groups of which
that ammunition is capable.
These ammunition refinements are
becoming important, particularly in
long-range matches.
The essentials of the tilted bullet were
discussed in detail no less than 50 years
ago by Dr. F. W. Mann in his book
"The Bullets In Flight". He pointed out that
the balance of the bullet and the spiral
path of the center of gravity are of
high importance in accuracy.
Following a discussion between
George L. Jacobsen of Frankford Arse-
al and the writer at the 1959 National
matches, a trial of the effect of neck
concentricity was carried out by Jacob-
sen. He described his results in ".30-’O6
Cartridge Cases And Accuracy", which
appeared in THE AMERICAN RIFLEMAN,
January 1960, page 20.
SEATING TOOL A FACTOR
The effects which Jacobsen found,
though small, are essentially in agree-
ment with the work reported here.
However, he did not separate the effects
of neck eccentricity and the bullet cen-
ter-of-gravity location with respect to
the bore. The angular direction of the
bullet seating tool is a controlling factor
in the initial position given to the bullet,
rather than merely case neck eccen-
tricity. Case necks can be centered or
eccentric, and the bullet can be inclined
in completely random directions. The
tilted bullet is believed to be the main
cause for center—of-gravity side shift.
The cal. .30 boattail bullet of 173 grs.
weight was selected for these tests be-
cause it is in common use and is of
sufficiently high quality for use in the
National Matches.
Using the gauge shown, 42 ammuni-
tion lots were sampled and the high
point was marked on each round gauged.
These rounds were grouped in steps of
.OO1" bullet tilt, and the data tabu-
lated. The results gave a bell—shaped
curve for 829 rounds of match ammu-
nition, peaking at about .0O2" (see
illustration). Measurements on Service
ball ammunition produced a curve of
similar shape, but peaking at about
.0025" tilt.
This graphically illustrates that even
match-grade ammunition has appreci-
able variations. There is a large spread
among particular lots and boxes. In
general, 10% to 20% of each lot, de-
pending on ammunition quality, falls
into .0O3", .0O4" or even up to .O10"
tilt. Run-of-the-mill ammunition can
thereby enlarge groups to about twice
the size which the same ammunition
can show when it is gauged before firing.
Since the tilt angle of the bullet is
so small (about 1/4 °) it is difficult to
perceive visually. The gauge, however,
makes the sorting a fast, routine step.
A mathematical solution of this prob-
lem was also tried (see box) and is in
good agreement with the results ob-
tained. It is gratifying to find the math-
ematical solution and the experimental
results in agreement.
MATHEMATICAL SOLUTION
A laterally displaced center of
gravity moves through the rifle bore
in a helical (screw) path. The pitch
of this helix is the pitch of rifling,
and its radius is the lateral displace-
ment of the center of gravity. On
leaving the muzzle, the center of
gravity continues in the direction it
had at that point. For example, if it
leaves at top of the bore and rifling
is to the right, the departure will be
to the right. The bullet travels ap-
proximately 2l.5" in a 24" barrel,
making 2.15 turns in the 10" twist
of rifling. The number of turns
shows the orientation on emergence
compared with that in the chamber
before firing. The angle of emer-
gence is that angle whose tangent is
2 pi times the lateral displacement
divided by the rifling pitch. For
.004" point displacement and I0"
rifling pitch, the tangent is 1/8(2·pi)
(.004)/l0 and the corresponding
angle is 1.1 minutes.
The displacement on target from
this cause is proportional to the
range and can be obtained without
noting the angle. For example, ,004"
point displacement gives in l0"
rifling pitch, so far as this mecha-
nism goes, a target displacement at
100 yds. (3600") indicated by the
proportion .00l· pi /10=X/3600, from
which x =1.1".
Attachments
The truth here is to get real honest results you have to take the shooter and any wind conditions out of the equation.
That being said, knowing that you have done everything possible to eliminate error in your reloading and equipment set up leaves only 1 factor to deal with, the human behind the trigger!!
That being said, knowing that you have done everything possible to eliminate error in your reloading and equipment set up leaves only 1 factor to deal with, the human behind the trigger!!
jackieschmidt
Gold $$ Contributor
As a side note, I have watched shooters use loaded round straighterners such as the Bruno, using substantial hits to “straighten” the thing out.
I ask……”how do you know you aren’t bending the bullet”.
I ask……”how do you know you aren’t bending the bullet”.
THIS ^^^ and what, XTR and Clark, have to say, in their Post's, are MY,. "thought's",.. EXACTLY and "Key" idea's for good, CONSISTENT,.. Accuracy. And WHY, I won't use, .006 to .09, TIR, "out of Round", Bullets for IMPORTANT ( Elk , Deer, Antelope, or, Moose, ) shots at,.. "Longer ranges". Then, you ADD IN, the WIND Factor, so WHY ,. "chance it" ??
"Plink" with, the "Junk" Ammo !
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Hmmmm??? My thoughts regarding this question is this: Just as when spinning an imbalanced top or ceiling fan or with the spin of a clothes dryer, a bullet that's not fully balanced (like due to some uneven deformation from the way it engaged the lands) will not have as much wobble when spinning as a high rate of speed as it does when the spin slows down. Therefore, a cartridge with a bullet having something like .006 TIR has little effective wobble from its imbalance (pretty stable) at 100 yds. due to its high rate of spin, but there's a much greater effective wobble at 1,000 yds. as the spin has slowed down substantially. So it seems to me that when shooting 100-200 yds. a lot of runout need not be of much concern, but when shooting long or extreme distance, you want to be close to perfect as possible. But if one is inclined to OCD with cartridge prep, it doesn't matter. 
Last edited:
It is the opposite. Gyroscopic stability increases with range, given adequate initial spin. General Hatcher demonstrated this in his 1947 work, "Hatcher's Notebook".Hmmmm??? My thoughts regarding this question is this: Just as when spinning an imbalanced top or ceiling fan or with the spin of a clothes dryer, a bullet that's not fully balanced (like due to some uneven deformation from the way it engaged the lands) will not have as much wobble when spinning as a high rate of speed as it does when the spin slows down. Therefore, a cartridge with a bullet having something like .006 TIR has little effective wobble from its imbalance (pretty stable) at 100 yds. due to its high rate of spin, but there's a much greater effective wobble at 1,000 yds. as the spin has slowed down substantially. So it seems to me that when shooting 100-200 yds. a lot of runout need not be of much concern, but when shooting long or extreme distance, you want to be close to perfect as possible. But if one is inclined to OCD with cartridge prep, it doesn't matter.
Brian Litz has an interesting discussion about this and a few other things reloaders seem to obsess over. He says that in his lab, they tested many calibers with run out as high as .008" and it made no measurable difference in groups sizes or accuracy.
Brian Litz has a good discussion about this topic and other practices that reloaders obsess over that really dont have any measurable differences in group sizes or accuracy. And explains that the time saved by not doing those things should be spent on marksmanship techniques like wind reading and things like that.Oh my God. Really?
I've been agonizing over this since I started using some new Redding dies a couple months ago and have worse run-out than I used to with my Lee dies. With those, I'd usually get 0.001-0.002 tir, and an occasional 0.003. With my Redding, I'm getting a wider range and a lot more at and above 0.002 with a couple 0.004.
I mean... My reloading the last couple of weeks has been more stressful and aggravating than enjoyable due to this. And you guys are telling me it doesn't matter much below 0.009 and no difference below 0.005?
The problem with Litz's proclaimation is that it's entirely empirical. There is exactly zero way to establish a threshold for the start of a causal relationship since the moment of bullet release takes place well after the initiation of a chain of interrelated events which we lump under the unhelpful heading of internal ballistics. As well, pinning the discussion to total indicated runout from base to tip helps to make the analysis doubly meaningless as the bullet is going to possibly be at an angle to the central axis of the case along its length and the seating depth will add even more variables to the equation. One cannot normalize this kind of complex system very well enough for a cause-effect relationship to be successful much less predictable.
To be clear, while what Litz says is no doubt true (he is a very intelligent and knowledgeable individual) inasmuch as the experimental data indicates it under the limited set of barrels/bullets/etc... used, there can be no cause-effect relationship established as the noise to signal ratio is not going to be kind to any efforts at statistical analysis unless the sample sizes used to make the connection and establish the existence of a real threshold at all would need to be exceedingly large not just in bullets and cases but also in barrels and every other component.
I think the short and sweet answer is the same as it is for SD's and CBTO and everything else we nerds obsess pointlessly over: Minimize your TIR but don't get all caught up in it. There are bigger fish to fry and getting all sweaty about something that small means that you're almost certainly missing the chance to obsess over something more important and more easily fixed, like how much coffee one has before sitting down to fire a group.
As an aside... is anyone else thrown completely off by how respectful this potentially extremely contentious discussion is? I'm just not used to it. Perhaps one of you would call the rest of us idiots for no apparent reason just to make it a little more familiar with respect to typical interweb forum discussions on any point of fact.
Alex Wheeler
Site $$ Sponsor
I have tested this a few times over the years. I always wanted to prove it mattered, but oddly every time I shot my worst vs my best the worst has always out grouped my best by a slim margin. Its not even something I measure anymore.
jvw2008
Lose the Second and we lose them all.
Or changing neck grip relative to a concentric round that isn’t “straightened”.
When you seat a non-concentric bullet into the lands and it’s concentricity improves, two things have to happen: 1) the jacket at the bearing surface behind the ogive has received more deforming pressure on the side first contacting the lands during chambering, and 2) for the bullet to be pushed into a more concentric position within the case, neck grip has been disturbed by axial movement of the bullet. Maybe neither of these events change the consistency of bullet shape or neck grip enough to show up on target because the affect is so subtle
I tend to favor this last though since I have lost matches with very concentric rounds and won a few with non-concentric rounds that I expected to perform poorly. For me today, if it’s under 0.002 I don’t worry about it, but I also don’t try to straighten it either.
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