Hornady Lock-N-Load Overall Length (OAL) Gauges - Manual (Page 2)

The initial distance a bullet travels is critical to an accurate handload. Any
loss of alignment, as the bullet travels from the cartridge case to the rifling,
will affect accuracy. Minimal changes in clearance (free-travel), between the
bullet and the rifling will often yield substantial improvements in accuracy.
The O.A.L. Gauge is an easy-to-use precision tool. It allows the user to (1)
determine maximum overall cartridge length (O.A.L.) from any firearm and (2)
produce handloads with a precise bullet seating depth while providing exact
bullet free-travel to the rifling. The O.A.L. Gauge will (3) monitor throat erosion,
and (4) check new or used firearms for freebore condition, a prime factor in
firearm accuracy. The O.A.L. Gauge uses your bullets for utmost precision.
The O.A.L. Gauge is sensitive and accurate enough that variations in operating
technique or grit and carbon in the throat can produce variations in your
results. It’s a good idea to clean the barrel before you begin, then spend a few
minutes to develop a technique that will produce a repeatable result. With a
little experience, it will take but a minute or two to determine a proper free-
travel and resulting bullet seating depth with any bullet you select.
Modified Cases are required to use the O.A.L. Gauge. They are available from
Hornady to fit popular firearm chambers (see listing), and are kept within
SAAMI specifications. Wildcat, Ackley Improved, and tight-neck chambers,
require that your cartridge brass be factory “modified” for use with the O.A.L.
Gauge. To order, see procedure on reverse side. Modified Cases are threaded
at the case head to attach to the O.A.L. Gauge. The case-neck is enlarged to
allow your bullet to slip freely within the neck. Chamfer/deburr both the
inside and outside of the Modified Case mouth to enable bullet
to slip freely. If in doubt of the fit of the Modified Case with your chamber,
insert the case into the chamber, then close the bolt. It must close freely
without distorting the case. DO NOT FORCE.
We are sometimes asked about headspace variations between the Modified
Case and the chamber. Generally the variation is a few thousandths. Many
handloaders choose to ignore the variation, as the O.A.L. Gauge provides
a more meaningful result than they have achieved with previous methods.
However, it’s easy to measure headspace variations using your caliper and a
Max. Cartridge Gauge or a Cartridge Headspace Gauge (Hornady makes an
excellent one.) Simply compare your fired brass with the Modified Case, then
“factor in” the variation, if it’s significant. Handloaders desiring absolute
dimensions can have their fire-formed brass “modified” by Hornady.
Do not place Modified Cases in a media type polisher, as the media will
become lodged in the threads making it difficult to remove. Also, do not
outside neck-turn Modified Cases in an effort to fit a tight-neck chamber.
This will result in the neck I.D. becoming too small to accept a bullet, which
ruins the case. If required, case necks can be reduced with emery cloth. DO
NOT RESIZE!
It’s a good idea to measure your bullets for length uniformity with your caliper.
Severely damaged or irregular bullet tips will produce overall length variations
when measurements are taken. Variations of .010" or more will produce
irregular O.A.L. results requiring the use of a suitable bullet comparator,
described later.
TO USE THE O.A.L. GAUGE: Remove the bolt or open the action to allow
access to chamber. Thread-on appropriate Modified Case to the O.A.L. Gauge.
Insert a bullet, with undamaged tip, deeply into the case mouth. Insert
assembly into firearm chamber, then slide bullet adjustment rod (plunger)
forward until contact with the rifling is felt. Lock adjustment rod in place with
thumb screw. The bullet will most often “stick” to the rifling. To remove the
O.A.L. Gauge assembly intact, gently push the assembly out, using a wooden
dowel or cleaning rod inserted from the muzzle.
We recommend using no more than 3 or 4 lbs. pressure on the bullet
adjustment rod (about that of a light trigger pull). Then, gently tap the bullet
adjustment rod with your index finger to ensure the bullet is in light contact