I’d like to know what an acceptable concentricity reading would be for a hunting application. I recently bought a new .300 Win Mag & when doing so I purchase some Federal Premium w/ 180 grain Accubonds. I ran them through my concentricity gauge & I cannot say that I was overly impressed with the results. Additionally I loaded up some ammo from virgin brass & found once again the concentricity not nearly as good as I get with a lot of my other loads (ie. .260 Remington and .308). Seeing how I am only going to use this rifle for hunting & that I will not be taking a shot past 400 yards, what is an acceptable concentricity reading?... and at what point would poor concentricity show up on a 400 yard target.
- Thread starter TBass
- Start date
Re: Acceptable concentricity for hunting
I tested some loads in my 300WM with no run out and .005" run-out. The .005" group was a little bigger, but I didn't see enough to make a difference on it. I would think anything under .006 or .007 would be alright. Any more than that, and it's in there pretty crooked! You can take your fingers and try to "bend" the bullet to straighten out the case neck. I've done this on some of my neck sized loads.
I tested some loads in my 300WM with no run out and .005" run-out. The .005" group was a little bigger, but I didn't see enough to make a difference on it. I would think anything under .006 or .007 would be alright. Any more than that, and it's in there pretty crooked! You can take your fingers and try to "bend" the bullet to straighten out the case neck. I've done this on some of my neck sized loads.
Re: Acceptable concentricity for hunting
I have often wondered how much it matters in a good straight chamber. I think that the Ctg will straighten out and just have a small amount of stress in a tight, straight chamber.
???
I have often wondered how much it matters in a good straight chamber. I think that the Ctg will straighten out and just have a small amount of stress in a tight, straight chamber.
???
Re: Acceptable concentricity for hunting
"I’d like to know what an acceptable concentricity reading would be..."
There is no "industry" or "common use" standard for acceptable concentricity; whatever each loader accepts is acceptable to him. Tight chambers and tight throats will limit the maximum possible runout at some point but that's an individual rifle thing. Bottom line, when we get the accuracy we can live with, it's good enough. A lot of other things must come into play first. Zero runout on a bad shooting load won't help much.
"I’d like to know what an acceptable concentricity reading would be..."
There is no "industry" or "common use" standard for acceptable concentricity; whatever each loader accepts is acceptable to him. Tight chambers and tight throats will limit the maximum possible runout at some point but that's an individual rifle thing. Bottom line, when we get the accuracy we can live with, it's good enough. A lot of other things must come into play first. Zero runout on a bad shooting load won't help much.
Re: Acceptable concentricity for hunting
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">
"The NRA Handloader's Guide" 1969 enlarged and revised from "The
American Rifleman" with article copyrights from 1950 - 1968
"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".
</div></div>
What does it all mean?
The bullets's center of gravity [or center of angular momentum or whatever] will be off the center of the bore if the bullet enters the bore crooked.
That and riflings causes centrifugal force that throws the bullet off course when it exits the muzzle.
I believe that the reason that my off center chamber is not much of a problem is because it throws the bullets off center in the same direction making a small group, while eccentric ammo is inserted in the chamber with random rotational orientation.
The chamber will bend ammo straight. Therefore, bent ammo can only get up to 2 moa error with .004" run out, and any worse still gets 2 moa error.
Very tight chambers, would then not be as susceptible.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">
"The NRA Handloader's Guide" 1969 enlarged and revised from "The
American Rifleman" with article copyrights from 1950 - 1968
"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".
</div></div>
What does it all mean?
The bullets's center of gravity [or center of angular momentum or whatever] will be off the center of the bore if the bullet enters the bore crooked.
That and riflings causes centrifugal force that throws the bullet off course when it exits the muzzle.
I believe that the reason that my off center chamber is not much of a problem is because it throws the bullets off center in the same direction making a small group, while eccentric ammo is inserted in the chamber with random rotational orientation.
The chamber will bend ammo straight. Therefore, bent ammo can only get up to 2 moa error with .004" run out, and any worse still gets 2 moa error.
Very tight chambers, would then not be as susceptible.
Re: Acceptable concentricity for hunting
I think one could safely glean, that this is one of the inherent problems
with sabots. Is it not??
I think one could safely glean, that this is one of the inherent problems
with sabots. Is it not??
Re: Acceptable concentricity for hunting
Guys I really appreciate the input. The concentricity on the factory new ammo was right at .005 to .007 as well as when I reloaded it. On the virgin brass I once again saw the same .005 to .007 on the first time that I loaded it, as well as when I reloaded it. All in all I am seeing .005 to .007 run out regardless…. And after running right around .002 on my .260 ammo that I use for long range shooting, I want to know if the .005 to .007 would realistically cause an issue for hunting.
So is the consensus that ammo w/ concentricity of .005 to .007 would not be that big of a factor hitting the vitals of a deer size target out to 400 yards?
I would normally answer this question myself by simply going out & shooting it; however, it is going to be a couple of weeks before I get that opportunity.
Guys I really appreciate the input. The concentricity on the factory new ammo was right at .005 to .007 as well as when I reloaded it. On the virgin brass I once again saw the same .005 to .007 on the first time that I loaded it, as well as when I reloaded it. All in all I am seeing .005 to .007 run out regardless…. And after running right around .002 on my .260 ammo that I use for long range shooting, I want to know if the .005 to .007 would realistically cause an issue for hunting.
So is the consensus that ammo w/ concentricity of .005 to .007 would not be that big of a factor hitting the vitals of a deer size target out to 400 yards?
I would normally answer this question myself by simply going out & shooting it; however, it is going to be a couple of weeks before I get that opportunity.
Re: Acceptable concentricity for hunting
Not sure what tools you are using, but if you don't have a Lee Neck Sizing Collet Die you might want to try one out. They are cheap and they work outstanding. I run all my cases through my Lee neck sizer and the most runout I have ever seen on any case I have ever loaded was .002. I check all my loads for concentricity. It doesn't matter if they are target or hunting.
Can anyone else support this?
Just my two cents.
Not sure what tools you are using, but if you don't have a Lee Neck Sizing Collet Die you might want to try one out. They are cheap and they work outstanding. I run all my cases through my Lee neck sizer and the most runout I have ever seen on any case I have ever loaded was .002. I check all my loads for concentricity. It doesn't matter if they are target or hunting.
Can anyone else support this?
Just my two cents.
Re: Acceptable concentricity for hunting
I realize there is a lot that I could do to address the concentricity and reduce it; however, I am really not interested in chasing down bench rest accuracy. This potentially will be a backup gun for a hunt that I am taking this fall. Ultimately I am just trying to ascertain if a concentricity of .005 to .007 alone would cause problems with hitting the vitals of a deer sized target out to 400 yards. If there is a strong belief that this is gong to cause problems then there is little reason for me to take substandard ammo to go & work up my dope in a couple of weeks.
I realize that there are a lot of intangibles, such as the overall accuracy of the gun, the shooter… and the lists goes on, but would the concentricity issue alone be such an issue that should be addressed before going to work up my dope.
I realize there is a lot that I could do to address the concentricity and reduce it; however, I am really not interested in chasing down bench rest accuracy. This potentially will be a backup gun for a hunt that I am taking this fall. Ultimately I am just trying to ascertain if a concentricity of .005 to .007 alone would cause problems with hitting the vitals of a deer sized target out to 400 yards. If there is a strong belief that this is gong to cause problems then there is little reason for me to take substandard ammo to go & work up my dope in a couple of weeks.
I realize that there are a lot of intangibles, such as the overall accuracy of the gun, the shooter… and the lists goes on, but would the concentricity issue alone be such an issue that should be addressed before going to work up my dope.
Re: Acceptable concentricity for hunting
I don't waste time checking run-out for hunting loads.
Unless, its for long range groundhogs or prairie dogs over 600yds.
Terry
I don't waste time checking run-out for hunting loads.
Unless, its for long range groundhogs or prairie dogs over 600yds.
Terry
Re: Acceptable concentricity for hunting
It measures the runout and you can remove it to under .0005" if you like. With practice, your runout can be "zero" if you like. I have one and it made a difference in the rifle I used it for.
http://benchrest.com/hnh/
It measures the runout and you can remove it to under .0005" if you like. With practice, your runout can be "zero" if you like. I have one and it made a difference in the rifle I used it for.
http://benchrest.com/hnh/
Re: Acceptable concentricity for hunting
I recently bought a Bersin Concentricity gage/fixer for my 7mm RemMag ammo and this will also do 30'06 and 300WM on the opposite side of the polymer body. It will handle other calibers in that size range and isn't limited to those three.
It uses a Swiss made dial indicator that measures to 4/10,000ths (.4/1000ths) between marks and these marks are wide enough to get it down to half that.
My personal goal is to 'get/fix' my ammo used for target shooting, down to three places, for a total indicated runout of 1.2/1000ths. This isn't hard to do.
They're not cheap, but they are repeatable and accurate and allow the reloader to fix the TIR, after the fact. One gage will work in all of their bodies, so you can cut the cost down.
I plan on getting bodies for 223/308 and either the 338LM (Nordic body) or the 22-250/220 Swift body, as I shoot 22-250. The gage on the latter measures down to 2/10,000ths, so it's pretty tight.
For basic, less formal shooting, +/- 8/10,000ths is fine, for a TIR of 1.6/1,000ths.
Chris
I recently bought a Bersin Concentricity gage/fixer for my 7mm RemMag ammo and this will also do 30'06 and 300WM on the opposite side of the polymer body. It will handle other calibers in that size range and isn't limited to those three.
It uses a Swiss made dial indicator that measures to 4/10,000ths (.4/1000ths) between marks and these marks are wide enough to get it down to half that.
My personal goal is to 'get/fix' my ammo used for target shooting, down to three places, for a total indicated runout of 1.2/1000ths. This isn't hard to do.
They're not cheap, but they are repeatable and accurate and allow the reloader to fix the TIR, after the fact. One gage will work in all of their bodies, so you can cut the cost down.
I plan on getting bodies for 223/308 and either the 338LM (Nordic body) or the 22-250/220 Swift body, as I shoot 22-250. The gage on the latter measures down to 2/10,000ths, so it's pretty tight.
For basic, less formal shooting, +/- 8/10,000ths is fine, for a TIR of 1.6/1,000ths.
Chris
Re: Acceptable concentricity for hunting
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RJ Hunter</div><div class="ubbcode-body">What do they look like on paper. Who cares what the gauge says. I've never seen a deer, elk, etc.. that knew how to check for case run out. </div></div>
I guess it all depends on how far that freakin' deer was, doesn't it?
SIG and the Austrian Ammo Federation did extensive testing on runout in atmospherically controlled underground tunnels at 300m and with moderate to high runout, and their findings would be the difference between hitting the vitals, or not.
I measured one 7mm RM round that had 12/1,000ths of TIR, which is pretty crooked, if you ask me. Most of my stuff using STD FL and sizing dies were between 4-8 thous. Batches made with a Redding Body, Neck Bushing and MicroSeating/Inline die, were between 2-6 with some being below two, in a sample size of I think 40, it was.
I got them all down below 1.6 thous, IIRC.
Chris
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RJ Hunter</div><div class="ubbcode-body">What do they look like on paper. Who cares what the gauge says. I've never seen a deer, elk, etc.. that knew how to check for case run out. </div></div>
I guess it all depends on how far that freakin' deer was, doesn't it?
SIG and the Austrian Ammo Federation did extensive testing on runout in atmospherically controlled underground tunnels at 300m and with moderate to high runout, and their findings would be the difference between hitting the vitals, or not.
I measured one 7mm RM round that had 12/1,000ths of TIR, which is pretty crooked, if you ask me. Most of my stuff using STD FL and sizing dies were between 4-8 thous. Batches made with a Redding Body, Neck Bushing and MicroSeating/Inline die, were between 2-6 with some being below two, in a sample size of I think 40, it was.
I got them all down below 1.6 thous, IIRC.
Chris
Re: Acceptable concentricity for hunting
Chris - did they define moderate to high run out in that experiment?
FYI - I too own a Bersin tool; however, I have some general concern that when fixing the concentricty using the Bersin tool that you are in turn effecting the seating tension... and I question if it is almost counter productive to use the Bersin tool.
I am interested if they defined moderate to high run out in that experiment
Chris - did they define moderate to high run out in that experiment?
FYI - I too own a Bersin tool; however, I have some general concern that when fixing the concentricty using the Bersin tool that you are in turn effecting the seating tension... and I question if it is almost counter productive to use the Bersin tool.
I am interested if they defined moderate to high run out in that experiment
Re: Acceptable concentricity for hunting
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TBass</div><div class="ubbcode-body">Chris - did they define moderate to high run out in that experiment?
FYI - I too own a Bersin tool; however, I have some general concern that when fixing the concentricty using the Bersin tool that you are in turn effecting the seating tension... and I question if it is almost counter productive to use the Bersin tool.
I am interested if they defined moderate to high run out in that experiment </div></div>
I don't know about you, but I'd rather have a bullet starting down my bore as straight as possible, than have a bullet leaving a neck with an immeasurably lighter pull.
They state factory runout can be anywhere from 4-20 thous, with some being as high as 40 thous. I gather that they measured factory ammo to come to this conclusion. I don't own any factory 7 RM, 30'06 or 300 WM to test out. I'm also assuming that they used factory ammo in their tests, but the notes on the targets are in German and it doesn't seem as if they list any control info on said targets, other than the basic stuff: date, control #, bullet holes, distance and I think weapon type.
They show targets fired with fixed and unfixed ammo at 300m/335yds. Their claim is that, at the high end of the scale, groups can be reduced by 50%, after virtually eliminating runout with the Bersin tool.
In the product literature and the reviews I have from VERY HIGH POWER '04, #1 and Precision Shooter April, '04, they address the problem of neck tension being affected. It seems that unless a person is wrenching on the bullet tip, going back and forth, with a lot of pressure, they're won't be an issue neck tension decreasing.
I had one or two rounds, in the beginning, that I vacilated on, maybe stretching things a bit, but it's wasn't like the bullet could be twisted out of the neck. Mostly, it's a couple of minute nudges and unless your brass is neck turned, annealed perfectly and inside reamed, your necks will have varying tensions, anyhow.
I haven't gone out and shot the 7 RM and I didn't leave any control groups, as I was practicing on the 65-70 rounds I had loaded up, but I think it's a good enough tool for me to forego buying an independant concentricity gage and good enough for me to spend another $350 on at least two more bodies.
Chris
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TBass</div><div class="ubbcode-body">Chris - did they define moderate to high run out in that experiment?
FYI - I too own a Bersin tool; however, I have some general concern that when fixing the concentricty using the Bersin tool that you are in turn effecting the seating tension... and I question if it is almost counter productive to use the Bersin tool.
I am interested if they defined moderate to high run out in that experiment </div></div>
I don't know about you, but I'd rather have a bullet starting down my bore as straight as possible, than have a bullet leaving a neck with an immeasurably lighter pull.
They state factory runout can be anywhere from 4-20 thous, with some being as high as 40 thous. I gather that they measured factory ammo to come to this conclusion. I don't own any factory 7 RM, 30'06 or 300 WM to test out. I'm also assuming that they used factory ammo in their tests, but the notes on the targets are in German and it doesn't seem as if they list any control info on said targets, other than the basic stuff: date, control #, bullet holes, distance and I think weapon type.
They show targets fired with fixed and unfixed ammo at 300m/335yds. Their claim is that, at the high end of the scale, groups can be reduced by 50%, after virtually eliminating runout with the Bersin tool.
In the product literature and the reviews I have from VERY HIGH POWER '04, #1 and Precision Shooter April, '04, they address the problem of neck tension being affected. It seems that unless a person is wrenching on the bullet tip, going back and forth, with a lot of pressure, they're won't be an issue neck tension decreasing.
I had one or two rounds, in the beginning, that I vacilated on, maybe stretching things a bit, but it's wasn't like the bullet could be twisted out of the neck. Mostly, it's a couple of minute nudges and unless your brass is neck turned, annealed perfectly and inside reamed, your necks will have varying tensions, anyhow.
I haven't gone out and shot the 7 RM and I didn't leave any control groups, as I was practicing on the 65-70 rounds I had loaded up, but I think it's a good enough tool for me to forego buying an independant concentricity gage and good enough for me to spend another $350 on at least two more bodies.
Chris
D
Deleted member 10043
Guest
Clark, do you agree with the information you posted? It is an interesting article/study summary.
Yes, Clark, I’d also would like to hear your thoughts on the matter.
918V. It has been a long time.
The curious thing about concentricity is that it is much more important in ammo than in chambering. Eccentricity in the chamber is consistent and throws all the bullets into the same small off center group. Eccentricity in ammo usually has random radial orientation when inserted in the chamber and so causes that maximum error in group size.
This is counter to human nature when we want to put extra effort in non recurring tasks [dialing in the barrel before chambering] and minimum effort in recurring tasks [reducing neck bend and neck thickness run out].
The guns I build and ammo load are not what is holding ME back. I have the bore concentric and parallel with the lathe spindle within 0.001". I use honed out forster sizers, sliding sleeve seater dies, and Lee collet neck dies. I am using Nosler, Lapua, and RWS brass. I am using Nosler bullets. My problems are more likely:
1) Wind doping
2) recoil reaction consistancy
3) trigger jerking
4) glaucoma [ scopes look cheap through my right eye]
5) Copper fouling
I put 4 deer in the freezer last month. I am not going to the range very often. I practice long range by myself for a week or two before hunting season. I shot buck at 625 yards. That is a long shot for me. The sure things are below 500 yards. There is a big difference between me and someone who shoots all the time.
The curious thing about concentricity is that it is much more important in ammo than in chambering. Eccentricity in the chamber is consistent and throws all the bullets into the same small off center group. Eccentricity in ammo usually has random radial orientation when inserted in the chamber and so causes that maximum error in group size.
This is counter to human nature when we want to put extra effort in non recurring tasks [dialing in the barrel before chambering] and minimum effort in recurring tasks [reducing neck bend and neck thickness run out].
The guns I build and ammo load are not what is holding ME back. I have the bore concentric and parallel with the lathe spindle within 0.001". I use honed out forster sizers, sliding sleeve seater dies, and Lee collet neck dies. I am using Nosler, Lapua, and RWS brass. I am using Nosler bullets. My problems are more likely:
1) Wind doping
2) recoil reaction consistancy
3) trigger jerking
4) glaucoma [ scopes look cheap through my right eye]
5) Copper fouling
I put 4 deer in the freezer last month. I am not going to the range very often. I practice long range by myself for a week or two before hunting season. I shot buck at 625 yards. That is a long shot for me. The sure things are below 500 yards. There is a big difference between me and someone who shoots all the time.
D
Deleted member 10043
Guest
That math is cool. Tangent » Degrees » MOA
Is there a linear relationship between eccentricity in the chamber and point of impact? Assuming the barrel is straight.
D
Deleted member 10043
Guest
According to this theory there is. It can get lost in the noise like shooter and the actual accuracy of the rifle and so forth. But it can at least be eliminated as a factor if used and corrected. It is up to the person to decide if it is important or not. Doing that math the deviation <.003 may be hard to spot for the average person.
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I really like the concept of this product... I have been kicking around the idea of the 21st Century concentricity measuring setup, but realized that no matter what it told me about the concentricity of my loaded rounds, I don't know what I could do about it. I'm using a CoAx press, so the case can "float" if it needs to in order to self-align with the die which also has a touch of float if necessary. I'm also using Forster non-crimping dies (for most of my ammo), so as far as seating goes, I'm doing everything that I know to do there, as well.
The H & H tool that you posted answers my question for me... if there's runout in the loaded round, there's a way to correct it. If you don't mind, about what did you have to pay for that setup?
While everyone has a different experience, I would expect that MOD ( Minute of Deer) would only be effected if someone was to see a TIR or over .009". For me, on my 308, a reduction of TIR from .01" to .002" has resulted in a change of 5 shot grouping in a standard Rem 700 ~.25". This are on the same day with the same rounds fired in a bore. This was a question that I had for myself and the people I load for/with. The more expensive rifle setups that my group has did not seem to be as effected, the custom cut barrels only gained .125" grouping improvement from what I could measure. Be aware that these results aren't perfect, but what I saw made it worth purchasing a concentricity gauge and spending time getting rid of TIR as much as I can. I do this on all rounds for my rifle now, I believe it is worth it, but again YMMV
When you say .005-007" runout, is the total indicated runout .010-014"? You need to divide TIR by 1/2 for the actual number. if your runout on a gauge is .006". your runout is .003". more than acceptable for hunting, even steel plate banging.
I picked up one of these TruAngle tools. Works well to get factory loaded ammo runout down.
http://www.trutool-equipment.com/TruAngle Guide.pdf
http://www.trutool-equipment.com/TruAngle Guide.pdf
Supposedly the above derivation of concentricity of ammo effect on precision has been verified. It is real, it is linear.... up to the point where the chamber bends the ammo straight.
Jamming the bullet into the lands will get at least the front of the bullet concentric in one plane normal to the bore.
Bart Bobbitt did this in 1997 when he shot a 20 shot 3.25" group at 800 yards with a 308.
But he had to get up early in the morning, when there was less wind.
But concentric in one plane is not good enough to keep the center of angular momentum of the bullet in the center of the bore. The bullet must also be parallel with the bore.
To do that, you will need some well prepared brass that locates on the shoulder of the chamber.
Jamming the bullet into the lands will get at least the front of the bullet concentric in one plane normal to the bore.
Bart Bobbitt did this in 1997 when he shot a 20 shot 3.25" group at 800 yards with a 308.
But he had to get up early in the morning, when there was less wind.
But concentric in one plane is not good enough to keep the center of angular momentum of the bullet in the center of the bore. The bullet must also be parallel with the bore.
To do that, you will need some well prepared brass that locates on the shoulder of the chamber.
