Datum Dial Instructions

User Manual: datum dial instructions

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1
User Instructions for the Datum Dial Ammunition Measurement System
(For Gathering Case, Bullet and Cartridge Length Data) Issue 3
1.0 GENERAL INFORMATION
The Datum Dial Ammunition Measurement System is an easy-to-
use and versatile tool that provides the data you need to refine
your case sizing and bullet seating operations (Figure 1).
Your benefits from gathering and analyzing reloading component
data are:
• Better accuracy because your ammunition’s headspace is
tailored to your firearms’ chamber.
• Safer shooting because excessive headspace, which may
lead to dangerous case separation, can be avoided.
• Quick sorting of batches of cases, bullets and cartridges to
effectively remove variation to provide relative consistency.
• More possible reloads because of reduced work hardening
of brass.
The core components are a body and three interchangeable dials
that, when used in a repeatable manner with your caliper, are
used to measure relative distances between selected points on
cases, bullets and cartridges (Figure 2).
Figure 2. Datum Dial Ammunition Measurement System
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Body
Case Dial
Bullet/
Cartridge
Dial #1
Bullet/
Cartridge
Dial #2
Figure 1. Datum Dial Ammunition Measurement System Uses
Relative Case Measurement
Relative Bullet or Cartridge Measurement
Provides a relative measurement (X) between the base of a
case to a datum point on its shoulder angle. May be used:
• Before sizing operations to find the optimal headspace for
your firearm (shown below and in Section 4.0).
• After sizing operations to check the set-up and/or
consistency of your reloading process.
Provides a relative measurement (X) from the base of a
bullet/cartridge to a point on the bullet’s ogive, very close to the
bullet’s major diameter. May be used:
• Before seating operations check factory bullet/cartridge
consistency (shown below and in Section 5.0).
• After seating operations to check the set-up and/or
consistency of your reloading process.
X
When this measurement is taken from several
cases that have been fire-formed from the
same firearm, and the total is averaged, it is
called the “Optimal Rifle Chamber Headspace”
for this particular firearm because it best fits
the firearm’s chamber.
X
X
Fire-Formed Cases
Optimal
Headspace
for Your
Firearm’s
Chamber
A B C D E
Base
Datum
Point
++++=
5
X
The “Optimal Rifle Chamber Headspace” measurement then
allows you to adjust your sizing die to produce cartridges with a
headspace fine-tuned for your particular firearm, ensuring that
the cartridge is tailored to your firearm’s chamber.
This measurement then allows you to adjust your seating die to
achieve the optimum distance from the bullet ogive to the lands of
the rifle. Obtaining the best bullet seating depth for a specific
bullet to be used in a specific firearm significantly improves the
accuracy of your loaded rounds.
2
Table 1. Datum Dial Ammunition Measurement System Order Guide
Order Number
Description
Use
DD1010
Datum Dial (Body with Case Dial already mounted), Storage Box
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Storage
Box
Measures the relative distance between:
• The base of a case to a datum point on its
shoulder angle.
DDKIT Kit: Datum Dial (Body with Case Dial already mounted),
Bullet/Cartridge Dials #1 and #2, Storage Box.
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Storage
Box
Measures the relative distance between:
• The base of a case to a datum point on its
shoulder.
• The base of a bullet or a cartridge to a point
on the bullet’s ogive.
DD1111
Bullet/Cartridge Dial #1
224 Cal (5.56mm)
243 Cal (6mm)
264 Cal (6.5mm)
284 Cal (7mm)
308 Cal (7.62mm)
Measures the relative distance between:
• The base of a bullet or a cartridge to a point
on the bullet’s ogive.
DD2222
Bullet/Cartridge Dial #2
172 Cal
204 Cal
257 Cal
277 Cal
338 Cal
DD7777
Blank Dial with five starter holes.
Allows you to custom-drill holes for diameters
not covered by the Case Dial or the two
Bullet/Cartridge Dials.
2.0 SAFETY INFORMATION
• Always wear safety glasses.
3.0 PREPARATION
1. Assemble the following:
• Material to be measured:
− At least five cases fired from the same firearm (known
as “fire-formed” cases). Ensure they are labeled to keep
them separate.
− Batch (lot) of bullets and/or cartridges. Ensure they are
from the same manufacturer.
• A good quality caliper.
NOTICE
PROPER CASE/CARTRIDGE PREPARATION TO ENSURE
ACCURATE MEASUREMENTS
• For fired cases: Use a straight-edge to check that the
primer is under-flush with the case head. If primer is over-
flush, deprime the case with a decapping-only die before
measuring with the Datum Dial and before re-sizing.
• For newly primed cases/cartridges: Use a straight edge to
ensure that the primer is under-flush and properly seated.
NOTICE
PROPER CALIPER USE
• Measurement when using a caliper is highly dependent on
the skill of the operator. Use a consistent, firm touch. Too
much force results in an under-indication; too little force
gives an over-indication. Consult an experienced machinist
for proper technique
• Ensure the caliper, as well as the item being measured, is
clean and free from debris
2. Review the following definitions. They are important for
understanding and using this product.
Datum
A reference plane, point or diameter that provides a base for
measurements and calculations.
Headspace
The distance from the face of the closed breech of a firearm to
the surface in the chamber which the cartridge case contacts
(seats). This distance differs slightly from chamber to chamber,
even within firearms of the same caliber.
Datum Line
Headspace
Receiver Bolt Cartridge
Bolt Face
Note that excessive headspace, which is excessive linear
endplay of a cartridge in the chamber with the bolt closed,
allows movement of the case during firing, which can cause
dangerous case stretching, case separation and gas leakage.
Excessive
Headspace
Cartridge
Bolt
3
Repeatability
The variation in measurements taken by a single person or
instrument on the same item and under the same conditions. A
measurement is repeatable when this variation is smaller than
an agreed limit. The conditions include:
• The same measurement procedure.
• The same observer.
• The same measuring instrument (caliper), used under the
same conditions.
• The same location.
• All measurements performed over a short period of time.
4.0 CASE HEADSPACE MEASUREMENT PROCESS
(Figure 3.)
Figure 3. Datum Dial Case Headspace Comparator
Components
6-32 X 1/2" Socket Head Cap Screw
(DD1010-017)
Washer, .250 X .156 X .013
(DD1010-019)
Case Dial
(DD1010-013)
Ball Detent
(DD1010-015)
Body
(DD1010-011)
Thumbscrew
(DD1010-014)
Cup Point Set Screw, 6-32 X 1/4”
(DD1010-018)
Step 1: Use Table 2 to determine the aperture/datum diameter
for your case.
Step 2.
Turn the Dial (DD1010-013)
so that the arrow lines up with
the selected datum diameter.
Step 3.
Position the Datum Dial
squarely against the movable
jaw of the caliper.
Step 4.
Gently, but firmly, close the
caliper on the Datum Dial.
Tighten the Thumbscrew.
Zero out the caliper.
Step 5.
Open the caliper. Insert the
case shoulder into the
selected datum diameter.
Step 6.
Rotate the case to remove
slack while centering the case
along the measurement axis.
Ensure the case is
perpendicular to the Dial.
Gently, but firmly, tighten the
caliper on the case head and
record the measurement in
Table 3.
Step 7: Measure the other four cases, record the
measurements and calculate the average. Remember:
repeatability is important when taking measurements.
Table 2. Aperture/Datum Diameters for Some Common Case
Calibers
Aperture/
Datum Dia.
Case Caliber
.330”
•
17 Rem.
•
204 Ruger
• 220 Swift
• 221 Fireball
• 222 Rem.
• 222 Rem Mag.
•
223 Rem.
•
6mmx45
.350”
•
22-250
•
22 Rem. BR
•
22 PPC
• 225 Win.
• 6mm Rem. BR
• 6mm PPC
• 6mm PPC/Wild
• 6mm Dasher
•
250 Sav.
•
6.5mm
GRENDEL
.375”
•
6mm Rem.
(224)
•
6x47 Lapua
•
6mm XC
•
25-06 Rem.
•
257 Roberts
•
6.5x 57
Mauser
•
6.5x47 Lapua
• 6.5x55
• 270 Win.
• 7x57 Mauser
• 280 Rem. (7mm
Exp.)
• 303 British
• 300 H&H Mag.
• 30-30 Win.
• 30-40 Krag
•
30-06
Spring./61A
Ackley
•
32 Win. Spec.
.400”
•
243 Win.
•
260 Rem.
• 270 WSM
• 7mm-08 Rem.
• 308 Win.
• 308 National Match
.420”
•
264 Win.
•
6.5-284
•
7mm Rem. Mag
•
7mm WSM
•
284 Win.
•
7mm STW
• 7mm Rem. Ultra Mag
• 300 Win. Mag.
• 30-338 Win. Mag.
• 300 Ultra Mag.
• 300 WSM
• 8mm Rem. Mag.
• 338 Win. Mag.
• 375 H&H
Table 3. Measurement Table
Fired
Case
Measurement Average Optimal Headspace
(A+B+C+D+E)/5
A
B
C
D
E
WARRANTY
All Forster Products are warranted against defects in materials and workmanship for the life of the product. Parts which, by nature of their function,
are subject to normal wear (such as springs, pins, etc.) and parts which have been altered, abused or neglected, are excluded from the warranty. If
the product is deemed defective by workmanship or materials, it will be repaired, reconditioned or replaced (at Forster Product’s option). This
warranty supersedes all other warranties for Forster Products whether written or oral.
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DD-1010-003 Issue 3, November 2012
5.0 BULLET/CARTRIDGE MEASUREMENT PROCESS
Step 1. Using Table 1, choose the Dial (DD1111 or DD2222)
that accommodates your bullet caliber.
Step 2. Change the Dial
1. Using the 7/64” hex wrench, unscrew the Socket Head
Cap Screw (DD1010-017) and Washer (DD1010-019) on
the top of the Body (DD1010-011).
2. Using the 1/16” hex wrench, loosen the Cup Point Set
Screw (DD1010-018) on the bottom of the Body one turn.
Remove the Case Dial (DD1010-013) and set it aside in
the storage box.
3. Assemble the selected Bullet/Cartridge Dial on the Body
and secure it with the Socket Head Cap Screw and
Washer. Ensure the Dial is snug against the Body.
Tighten the Cup Point Set Screw just enough to ensure a
firm rotation of the Dial.
Step 3.
Turn the Dial so
that the arrow lines
up with the
selected bullet
diameter.
Step 4.
Using the
Thumbscrew
(DD1010-014),
position the dial
squarely against
the movable jaws
of the caliper.
Step 5.
Gently, but firmly,
close the caliper on
the Datum Dial.
Tighten the
Thumbscrew. Zero
out the caliper.
Step 6.
Open the caliper.
Insert a bullet or a
cartridge into the
selected bullet
diameter.
Step 7.
Rotate the bullet or
cartridge to remove
any slack while
centering the case
along the
measurement axis.
Ensure the bullet or
cartridge is
perpendicular to
the Dial. Gently, but
firmly, tighten the
caliper on the bullet
or cartridge case
head and record
the measurement
as needed.
6.0 REPLACEMENT PARTS
Every product component is available individually. A complete
list of component order numbers and prices is available on our
website. Go to forsterproducts.com, then click on
Components/Parts Price List.
7.0 RESELLERS
We recommend using our Resellers when ordering our
products. Their experience and knowledge will help you select
the best products that meet your specific requirements. In
addition, they usually offer the best prices and convenient
delivery options.
To find a Reseller, go to forsterproducts.com, then click on
Locate a Reseller. If your Reseller cannot supply you, please
contact Forster Products directly.

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