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GUNS Magazine August 2012 Digital Edition - Page 22
STORY: Hamilton S. Bowen MeAsuriNG tooLs They’re needed for many shooting endeavors. B elieve 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 gunsmith to need measuring tools. 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, bullet diameters, head diameters, 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" increments. Micrometers are the most accurate hand measuring tools we 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. mortals can buy. The better ones will measure precisely, repeatably in .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 $100 to $200 for a good one. If you 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. Alas, not everything can be measured between a couple of flats so micrometers come in a variety 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. 22 W W W. G U N S M A G A Z I N E . C O M • A U G U S T 2 0 1 2