Case Necks
In my
last column, I talked about the importance of paying attention to the
cartridge case’s “ignition system” i.e. the flash hole and primer pocket.
This month, I thought I’d talk a little about the other end of the case -
the neck. Of course the neck is very important to accuracy because it
holds the bullet.
Right
up front we have to ask ourselves “Is this tedious procedure worth my
time?” Well, it all depends. If you’re shooting a Contender, Encore, or
similar firearm with a standard factory barrel (which are known for their
generous chamber dimensions and long, long throats) the chances are that
neck turning won’t do you a bit of good, so don’t worry about it. There is
an exception however which is based on the old saying “It’s never so bad
that it can’t get worse”.
Get out
your dial caliper, and check the wall thickness of some new brass cases
that you’ll use in your gun. However, before doing so, chamfer the inside
and outside of the case mouth first. New cases often have a little ridge
of metal that’s formed during the manufacturing process around the edge of
the mouth which will throw off your measurements if it’s not removed. OK,
check the neck’s thickness in at least four places. If there is a variance
of .0015” or greater from the high side to the low side, experience has
shown that it will negatively effect accuracy to a degree that it will be
worth your while to neck turn the cases. If the variance is less than
.0015, don’t bother.
On the other
hand, if you’re shooting a Contender, Encore, or other gun with a custom
tight fitting match chamber, it also is probably worth your time and
effort to neck turn your cases. The reason we want to do this is because
we want the bullet to be as closely aligned to the center of the bore as
possible when the cartridge is in the chamber. The more the bullet is off
set from the bore’s center line, the more lateral and/or vertical stress
it will be subjected to when it enters the rifling of the barrel. For
instance, did you ever get a screw misaligned in a threaded socket? Of
course. We all have. We’ve also on those occasions have sometimes (in
spite of our common sense) continued to turn the screw in even though we
knew it wasn’t lined up properly, using greater and greater effort to get
the d#%nn screw in there.
Ok,
similarly, when a misaligned bullet leaves the bore after being forced
under enormous stress into the barrel, it will immediately start yawing
around in response to that stress. The amount of yaw will be directly
proportional to the amount of bullet off set. While it’s yawing around
it’s also intermittently presenting a greater profile to what ever wind is
out there, and therefore will experience more wind deflection. Eventually,
the bullet should settle down and “go to sleep” - if the range is long
enough, but the damage to accuracy will already have been done. So, if we
have a match chamber, and/or if we determine that our brass is
significantly thicker on one side than the other, we’ll want to neck turn.
Now
there are a lot of neck turning tools out there and to be honest they all
do a good job, so it comes down to a matter of convenience and preference.
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"The Sinclair
1000 neck turning tool will help to fine tune your brass." |
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I’ve been using a Sinclair 1000 tool for many years and have been happy
with it except that the blade is easily adjustable going in but isn’t if
you want to adjust out. Additionally, it take three different allen wrenches
(supplied) to set it up. I would have preferred if it was just one size
wrench. Once it has been set up though, it’s very easy to use. Although
I’ve never used it, the new RCBS tool looks pretty nice and I’ve been
meaning to try it out sometime. However, no matter what tool you use, they
all work essentially the same i.e. the case neck fits on a mandrel and a
cutting blade removes the metal.
The
first thing we need to consider is the fit of the case neck on the
mandrel. That means that before we do any cutting, the case first has to
be sized. This is necessary because we just can’t have an expanded case
neck slopping around on the mandrel during the turning process.
Consequently, the expander ball of your sizing die should be anywhere
between .0005” and .0015” larger than the neck turning mandrel. We want a
fit where the neck will go over the mandrel with a smooth motion with just
a bit of drag. To that end, you’ll probably want to lube the mandrel with
a good case lube. I use Redding’s or some times RCBS’s. If your case neck
won’t fit over the mandrel, it means that your sizing die’s ball expander
is too small and the die is squeezing the neck down too far. Your best
option in those cases is to simply remove the mandrel from the cutting
tool and chuck it into an electric drill. Then take some emery cloth and
then polish the mandrel down to where it’s a smooth fit for the sized case
mouths.
Ok, now
take a case that you know is too thick on one side and clamp it into the
turning handle. Now insert the case neck onto the cutting mandrel. Next,
adjust the cutting blade down to where it just barely touches the brass on
the high side. Remove the case from the mandrel, and adjust the blade
down just a little bit more. Don’t over do it. Put the case back on the
mandrel and now start rotating the case forward under the blade. Go slowly
and observe how the blade is taking off just the highest of the high spots
on the brass. Be careful not to cut into the shoulder of the case. Ok, get
your calipers and measure the neck. If you’re still getting a variance of
more than .0015” from one side to another, move the blade down just a
little bit more and cut again. Repeat until the proper thickness has been
reached.
By this
time you’ve probably observed, that the areas that have been trimmed away
are a nice brilliant brass color, while the low spots that haven't been
touched by the blade are dull looking. It’s a great temptation to lower
the cutting blade even further down to trim away those low spots so the
entire neck looks nice and bright. DON’T DO IT! When that case is fired,
the chances are very good that the case neck is now way too thin for your
sizing die. As a result, the neck won’t be sized down enough (if at all)
to grip the bullet. The result is a ruined case. When neck trimming, it’s
very easy to over do things, so go slowly and carefully.
Once you have your
blade adjusted properly, lock it in place. It’s also not a bad idea to
keep a spare case which has been turned with the tool as a dummy so when
you have to readjust the tool after turning the cases for a
different gun/caliber/cartridge you can use the dummy to bring the blade
back to its original setting.
Last
point and reality check. Don’t expect a wild and dramatic improvement in
accuracy after neck turning. This procedure won’t turn a fair load into a
great load and it won’t turn an average shooting gun into a tack driver.
Nor is there any probable advantage when shooting at the regular full
sized targets. Remember, we’re talking about handguns held by people with
no use of artificial support who are shooting at fairly large targets.
Neck turning will provide an improvement, but we’re talking about a fine
tuning procedure here, not a miracle. It’s most valuable result will
probably be experienced when addressing the shoot off and half scale
targets. There, we need every fraction of an inch in accuracy that we can
get, and that’s where the pay off will definitely come into play.
Reloading Presses, Dies
& Concentricity
One piece of
advice you’ve seen in my scribbling many, many times over the years is that
when it comes to silhouette competition, buy the best that you can afford - no
matter what it may happen to be. In fact, I’ve often said “If you can, stretch
a little farther” to buy the best quality. In the case of optics, guns,
bullets etc. the principle is fairly obvious. However, when it comes to
reloading presses and dies, the principle is often forgotten because we tend
to take these things for granted i.e. a press is a press and a die is a die.
Not really.
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"Buying quality
dies like these will insure case concentricity." |
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If you’re
thinking about buying a reloading press or some dies (the two are parts of the
same mechanical system) and are thinking about an economy product, consider
the following.
A. How well is the press’s ram aligned with
the die on the top?
B. Is the shell holder machined perfectly parallel to the ram.
C. Is the shell holder machined perfectly parallel to the
surface of the die hole at the top of the press?
D. Is the de-capping rod located in the
exact center of the die?
E. Is the de-capping rod located in the
exact center of its lock nut?
F. Is the expander ball located exactly
centered on the de-capping rod or is it slightly offset?
G. Is the expander ball perfectly round or
is it slightly lop sided?
H. Is the top of the die hole on the press
perfectly parallel so the die isn’t cocked to one side when screwed in?
I. Is the die’s lock ring perfectly
parallel to the top surface of the press?
J. CRITICAL!!! Is the inside diameter of
the die concentric with the outside diameter?
K. Is the die’s de-capping rod perfectly
straight or is it slightly bent?
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"Precise tolerances
in a press add up to accuracy." |
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Does all
this really make any difference? You bet it does! If each one of these eleven
things was off by only half of one thousandths of an inch, we’d have a very
non-concentric case, and the accuracy of any ammo loaded with such a press and
dies would be definitely negatively affected.
Ok, that
being said, it’s also a fact of life that very few of us have the means or the
ability to check and measure all those features on our press and dies. So what
do we do? First, buy the best quality you can afford.
Second, to
see if we really do have a concentricity problem with our current press and
dies, we can check what it’s doing to our brass. To do so, we’ll need a dial
gauge and a fixture to hold the gauge and case. With all the Chinese tool
imports floating around, the cost of dial a gauge has really dropped to the
point that just about anyone can afford one. As far as the fixture is
concerned, there are a number of places to purchase them. Start at Sinclair
International and shop around.
Ok, now
take a couple of fired cases and clean the necks of any powder residue to
insure it won’t affect our readings. Place the case in the fixture and
position the dial gauge’s tip in the middle of the case neck and measure the
amount of run-out. Note the results on a piece of paper. (It should be close
to zero.) Now run a case into the neck sizing die with the de-capping rod and
its expander ball removed. Again measure the run-out. The difference between
the two readings will tell you the amount of run-out that the neck area of the
die is imposing on the case neck.
Now we want
to follow the same procedure with the de-capping rod with the ball expander
back in the die. This will tell you if it’s the de-capping rod assembly that
is causing the excessive run-out.
By taking
these two measurements, we’ll know what part of the die is giving us excessive
run-out (.004” or more). The die could:
-
- have an out of round
neck
-
- have residue build up
in the neck area (clean your dies)
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- have an off kilter
shell holder (try another)
-
- off center ball
expander
-
- out of round ball
expander
-
- bent de-capping rod
-
- cocked de-capping rod
-
- press problem
Borrow a
similar die from a friend to see if the problem is just your die. If so, call
the manufacturer. If not, call the press manufacturer. However, if you buy
quality, you probably won’t have a problem at all. If you can’t afford to buy
quality right away, save for it. Don’t settle for junk. Quality is always
worth the money.
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