Guns 2012-08.pdf - Jeffersonian

STORY: Hamilton S. Bowen
Measuring Tools
They’re needed for
many shooting endeavors.
Believe it or not, human beings do not think about
sex every waking moment. The other 10 percent of
our contemplative time is given over to pondering topics
like money, margaritas, why we are here or, in some rare
cases, the physical characteristics of our world. For gun
junkies, that world encompasses a lot of speculation
on height, width, diameter, distance, various spatial
relationships, etc. We’ll contemplate here a few of the
necessary tools useful in the satisfaction of our curiosity.
You do not have to be a practicing mortals can buy. The better ones
gunsmith to need measuring tools. will measure precisely, repeatably in
Shooters are always measuring group
sizes, hole spaces for scope mounts
of peep sights, length of pull and so
on. If you are a reloader, then you are
constantly measuring case lengths,
.0001" increments. Since more precise
measurements are an indicator of
importance, this is one place not to
scrimp on quality. You get exactly
what you pay for so expect to pay
bullet diameters, head diameters, $100 to $200 for a good one. If you
case wall thickness and the like. How
sophisticated your tools are depends on
the job to hand. Measuring cartridge
case length with a plastic caliper is fine.
Measuring case head expansion for
pressure signs requires a high-quality
blade micrometer graduated in .0001"
procure only one, the standard 0-1"
with flat anvil and spindle faces is the
most important. While digital tools are
now all the vogue, there is something
inelegant about them that leaves me
cold and uninspired. I like pretty stuff,
including tools.
increments.
Alas, not everything can be
Micrometers are the most measured between a couple of flats
accurate hand measuring tools we so micrometers come in a variety
Can’t have too
many measuring
tools around.
This pair of micrometers—tubing and blade
types—are used as often at the reloading bench
as the workbench.
of styles. The most important other
micrometer for use around a gun
shop or the reloading bench is the
tubing micrometer which has ball
anvil and a flat spindle for measuring
tube wall thickness or hole distances
from edges. Their obvious lower limit
on measurements is governed by
ball diameter. I use mine regularly to
measure cartridge case wall thickness.
Another helpful specialty micrometer
is the blade type for measuring into
narrow spaces like grooves or slots.
Mine has been used more for measuring
cartridge case web expansion at the
head in search of pressure-related
changes. Depth micrometers are critical
for measuring and setting headspace
when re-barreling a rifle.
Tricky Stuff
Measuring inside diameters is
trickier. Often, the simplest way to
measure hole diameters is with pin
gauges. Precise internal measurements
that would otherwise require some
exceedingly costly inside micrometers
can be determined to within a few ten
thousandths with simple pin gauges
available in .0005" size increments.
There are several tolerance types. The
handiest for most of us is the -.0002"
meaning that the pin is actually .0002"
smaller than indicated. If a .4530" pin
will pass through a hole but a .4535"
pin will not, you can be pretty sure the
hole is somewhere between .4530" and
.4535" since there must be a few tenths
of clearance for even a tight slip fit.
Not many things measured in a gun
shop need be determined that closely.
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WWW.GUNSMAGAZINE.COM • AUGUST 2012