Home Forums Hunting & Shooting Ask The Gunwriters Down the Bunny Hole of Concentricity

Whatever works for you.

True dat...but more accurately it's "whatever wins for me".

So it works for you.

Why don't you tell us abut your use of the Hornady Concentricity Tool then?

I use a NECO. In addition to the overall TIR, it also gives me the casewall/neck thickness variation (which is supposedly the source of a case ultimately taking a banana shape). These days, I tend to start off with good brass, and use the NECO to spot check for lot quality. If I chase another brand ie Alpha or Peterson like I'm tempted to then I'll take more extensive measurements. Last batch I worked up was the Lapua Palma. Typical Lapua quality. FWIW, I've had benchrest friends tell me they've regularly shot fantastic groups in the process of fireforming their virgin brass.

Okay. It appears you aren't familiar with the Hornady gauge specifically, but I'll bet Shaman would like to hear your thoughts on concentricity gauges generally. Remember, he is not shooting benchrest, so his use of the gauge, and what it can do for him are a bit different.

Did Shaman make a good choice WRT his gauge? If not, why not? What should he be looking for? Any tips that you could pass along to him?

Since he just got the gauge, I am sure he would appreciate any information.

Steve: You're right. Peering down this rabbit hole reminds me of my early caving days. There was a hole out back of the fieldhouse that used to steam in cold weather. You knew it was deep. You knew to stay away from it unless you were prepared. It was called the Screamin' Willy entrance, and it was where they got you checked out on vertical ascensions before letting you at the more technical stuff. In the beginning, they just warned you not to wander too far from the fieldhouse in that direction in the dark. Much later, you found yourself in your harness in the summer sun next to this hole in the ground looking at 65 feet of drop and wondering how the hell you got there, and wondering how you were going to get out. The blow coming up from the hole was cool, but it smelled rank from all the dead things that had fallen in.


As I stated in my followup blog post, I'm pretty sure I made a good choice for me for now.

1) I'm a hunter that shoots and not the other way around. That's slowly changing as the years go by. I'm beginning to enjoy shooting from the bench and loading at the bench as an end unto itself.

2) The Hornady does a good job of measuring runout.
3) It identifies the really crooked ones that might affect a group. I can segregate them.
4) It is proving in the cartridges I test that I don't have a runout problem.

If y'all would remember my posts from earlier in the year, I come from a planet where a 4MOA deer rifle is considered acceptable. This is where all "them grains 'n $hit don't mean nothin'" and "I hit what I aims at." are common statements. In the land of the blind, the one-eyed man is king.

Just as a thought.
Take a 4 of the best running ones in a proven gun/load set up and shoot them against say 4 of the ones that runout .005 to .007..
Test for grouping the way you would normally do.
At least that way you will know for sure, that the effort you are making, is worth it.

I have a old Sinclair run out checker and a tru angle tool.
The thing about the tru angle tool you have to be wary of, is over correcting the runout.
Over corrected rounds have less neck tension and accuracy will fubar you... I slight tweek tru angle good.
Push that bullet around some,,tru angle bad.

dave

Mr Redgwell,
Thank you for bringing me back to the OP's question. We are on different branches on the same tree of trying to produce the most accurate ammo within our capabilities. For me it's about intervening at a lower level by selecting better brass, dies, presses to produce better ammo. I've decided that my needs of volume, efficiency and accuracy mandate it ...but I'm a competitive shooter and not everyone is. Shaman is trying to correct and cull ammo after the fact for a hunting rifle. I think it's great that he is getting results he is happy with. We are approaching it with different needs and I have shared my perspective. I hope my perspective helps him and the others viewing at some point of their quest.

Yours and my comment about brass fired in a chamber might have bearing for the OP because it might give one the impression that fired brass can be eliminated as a source of runout. As I have stated above, that has not been my experience within the construct of my accuracy needs.

Shaman has titled this thread appropriately...it's a "bunny hole" and I'm speaking from within it. At some point he might be looking at case head squareness, neck and case wall thickness... and this is only one fourth of the system as I view it (the other three being rifle, sighting equipment and shooter).

I don't believe that most people realize reloading dies are responsible for almost all runout. Proper die set up is important.

For example, I check runout with my 308 brass after resizing, and again after bullet seating. That started in 1980. I had a new set of RCBS dies that weren't made quite right. Despite all my efforts and adjustments, they seated bullets crooked, but I didn't notice that initially. My groups got larger after buying the RCBS set. We were on the range and a friend said he had a gauge that would measure runout. Lo and behold, the gauge read 0.004 to 0.007. I tried revamping my set up, but nothing worked. I realized that I had to get a decent set of dies, so I replaced them with Redding. Down the road, I got a gauge, set of Forster dies, and a bushing bump die.

I learned that a quick check on the gauge would confirm that the dies were correctly set up. For Shaman, I would recommend a three point check.

1. Check runout of the fired cases before they are resized. This should show you that the necks are straight coming out of the rifle.
2. Check runout of the resized cases coming out of the die. This will show if you have the dies set up correctly (or that they were properly made).
3. Check runout of the cases after the bullets have been seated. This will show if you set up the seating die correctly, or may need a different seating stem.

For the overwhelming majority of hunters, the brass will be straight, coming out of the rifle. If the dies were properly made, you will be able to spot runout that is introduced by the resizing or seating dies. You can go back and confirm that your set up was correct.

There are other causes of runout, but I think the majority of it happens at the bench.

You don't have to check absolutely every case (unless you want to). If you have your dies correctly set up, and are starting with good brass, checking the first few is enough.

Shaman, if you're wondering like I bet many other people are, of how you're supposed to set up dies or check them, then look here for the answers...http://www.zediker.com/books/handloading/hlmain.html

or here......http://www.zediker.com/books/TGA/TGA_main.html

These are the best loading manual purchases you will ever make. There is an entire chapter on setting up and checking a set of dies.

Glen's books are among the best, but there are a number of other good ones, especially RIFLE ACCURACY FACTS by Harold R. Vaughan, or even THE BENCHREST SHOOTING PRIMER, published by Precision Shooting in 1997.

White I realize these are antiques compared to Zediker, they might be more useful to hunters, rather than target shooters.

I have both of those books, as well as many others in my collection, and Vaughan's book goes into fine detail about the effects of non-concentric rounds. It's well worth the read, and there's no need for anyone to try it out for themselves after reading it. I also looked through the entire contents of Benchrest Primer, and couldn't find any articles on die setup, but one that did was the Highpower section of Precision Shooting Reloading Guide. The only problem with that one is getting lucky enough to find one on ebay as cheaply as I did. Some of these manuals are extremely pricey on the open market.

Some of these books may be antiques, but they were still penned by guys who were the best at what they were doing, and their results have stood the test of time so I still seek some of them out just to see what insight they may have. One thing I have learned over the years is you usually have to look to multiple sources to find all the answers you're looking for, as no one seems to have all the bases covered in one place lol.

John: I just managed to snag a copy of The Benchrest Shooting Primer for $22 off Ebay. Rifle Accuracy Facts seems to have become unobtanium.

FC363: The Zediker books are all current, so I'm going to hold off until TBSP arrives. However, they're now on the list.

Steve: That's a good idea about measuring the brass.

ChrisF: Up until now, I had not given serious consideration to the brass. For 19 years, I've loaded with my major concerns being safety first followed by economy with accuracy being kind of a side benefit. I'd had a book on reloading for several years and been reading in it before I got my first press. It took quite a while to realize the author had hooks instead of hands. That was a sobering thought that sticks with me to this day. I generally load well below MAX, and don't try anything too jiggy.

Beyond that, I've tried to keep things on the cheap. I've only bought virgin brass when it was the only way. Normally I'll buy once-fired brass in bulk so I have consistency. If it comes mixed, I'll sort it by mfg. As a result, I load with a lot of other people's floor sweepings.

I'm not trying to disagree with you. I'm just trying explain where I'm coming from. This whole accuracy thing is somewhat new to me. At the recommendation of this august forum, I purchased a Ruger American Predator in .223 REM a few years ago with the explicit purpose of starting to investigate how accurate I could make ammo. So far, I've had some decent results, and it seems to be something I'll enjoy (probably more after I retire). By any sort of measurement, I'm past getting my toes wet. I'm now up to that point where the pool is licking at the bottom of my trunks, and any minute a wave my drench my short hairs.

I've got to get going for now. The wireless broadband has gone catawumpus at deer camp, and I'm using that as an excuse to drive down and have a look around.

Checking concentricty gives an opportunity to find out where in the loading process lack of concentricty/high TIR occurs. Once you find the problem you can fix it.
This process has led me to using a Redding body die, Lee Collet die and a Forester competition seating die. Run out is now only checked when new components (to me) are used.

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".

Shaman,
No offense taken. It's a journey, and you're on a different point than I am. I've had detours on trying to use budget equipment (to show that highpower rifle competition can be accessible without having to pay gobs of money...RCBS partner Press, Hornady dies, Lee measure etc.).

Mr Barsness,
I'm careful accepting Z's recommendations these days. I rated a mention in the first printing of his handloading book. He pulled it after we disagreed on how he was making his recommendations of his friends. I love Vaughn's book on the other hand because he defines the question, develops a test to try to shed light, and does it with a Rocket Scientist's expertise. He was a modern day Franklin Mann. There are broad take aways like concentricity matters and bullets don't take the big spiral path to the target that has been alleged by some. But as much as I love that book, there's not much on the nuts and bolts of handloading. Lots of why it might be worthwhile chasing certain processes though.

Clark,
That is a great article. For years I would hear the dogma of runout driving inaccuracy and a figure of 0.004. It took me years to run down the Abatiello article and it's companion Jacobson article where that 4 thou figure was quantified for the 30-06. It's worth noting that Jacobson worked for Frankford arsenal and did his testing out of a Mann fixture (barrel locked in a vise mounted to concrete) at 300 yards. I've found that 4 thou is a good starting point, but I believe the number varies with bullet type, distance and accuracy threshhold.

I'll offer a couple of other recommendations for reading if one were motivated to chase accurate reloading; Older American Riflemans were a wealth of accuracy articles (like the Abatiello and Jacobson articles). I like anything by Bill Davis and Creighton Audette. Audette in particular wrote about the detriments of brass that took a curvature because of uneven wall thickness, and was able to show how supporting the axis of the curvature with the plane of the bolt lugs improved accuracy (Vaughn btw was not able to replicate his results). Bill Davis wrote some very technical articles (he had a long career doing ballistics work for our arsenals and for his company Tioga engineering) but also wronte some very practical articles such as "should you worry about damaged tips on your bullets?" with testing to show the effects and "do off centered primer flash holes matter?".

Yes the neck wall thickness runout contributes to the concentricity error, unless the Lee collet neck die is used.

I believe if the bullet is seated long enough so it engages the lands in the chamber, then the bullet is concentric at that point along the bore.
To get the bullet parallel with the bore I need it concentric at another point. I assume the firing pin will push the cartridge forward until the cartridge shoulder centers in the chamber shoulder, much as a tang centers in a Morse taper or a collet centers in an R-8 mill. To measure this in the concentricity gage, I measure at the bullet ogive and rotate while located on the cartridge shoulder and another point near the rim.



Here you can see the Sinclair concentricity gauge I have modified so I can get the case shoulder rolling on the balls.

Back in the 1990s on rec.guns there was a professor Bradshaw saying he never touches his 6mmPPC brass with an expander ball when forming from 220 Russian.
So I asked him what his the difference between his madrell and an expander ball. He said it was push stroke vs pull stroke.

Chris,

I recommended those two books NOT so muchbecause of info on handloading concentric ammo, but because they contain plenty of valuable information on other aspects of accuracy, including shooting. This is because so many of the handloaders I know tend to think one simple thing is THE ANSWER which will result in tinier groups, which have somehow become the main point for most hunting handloaders--aside from more velocity, of course. But many who constantly dink with their handloads don't really have much clue about how to shoot off a bench accurately, or the effects of wind even 100 yards, or other stuff that might help them far more than going further down the rabbit-hole of concentricity.

Neither finer accuracy or another 100 fps matter all that much for most deer hunters, who rarely shoot over 300 yards and often not over 200. But modern hunting has become something of a gear sport, because most Americans live in "metropolitan statistical areas" where hunting usually involves a trip and, often, considerable money. Most can't hunt as often as they like to, so instead spend far more time fiddling with their hunting gear, especially rifles. This is why there's something of an obsession with tiny groups, even when they're of no real use to the hunter: They get to spend time in the loading room and at the range, which extends their hunting "season."

This is also why my collection of shooting literature includes not just the latest and greatest handloading info, but a bunch of other info, both new and historical,. In fact my collection of "rifle accuracy" books includes volumes that would be considered less than useless today, such as THE ULTIMATE IN RIFLE PRECISION, edited and partly written by Townsend Whelen. It was published in 1951, when benchrest shooters still tried to turn surplus 98 Mausers or old Winchester single-shots into winning bench rifles. There's even a chapter on adjusting double-set triggers. Is it applicable to today's hunting rifles? Some is, often far more than the info in recent rifle-accuracy books.

I write for hunters, and while I continue to collect books on all sorts of rifle subjects (along with a gun magazine collection that goes back over a century) I am far more interested in helping my hunting readers get more out of their rifles, often with far less specialized tools than benchrest and other target shooters would use. Which is why I include hints on how to make ordinary expander-ball dies produce straighter ammo--and still experiment with them to find ways to do so. Probably 95% of hunting handloaders use such dies, and that sort of info is far more useful to them than the latest techniques for making target ammo.

As I used to say to some of the staff when I was working, "Let me be the deliverer."

Some of the information in this thread is beyond what most of the readers here understand or can use. This is not a slight, but rather, an explanation of the audience.

***ChrisF, Followed***