G3 Rimfire Thickness Gauge
For accuracy-conscious handloaders
of centerfire ammunition, quality control is part of the reason we go to all the effort.
Chief among these controls is the ability to match each case to the chambers - at least in
loading for most rifles and single-shot pistols - even after some sizing of the case. The
rimfire shooters among us must forego all that, both the effort and pleasure of reloading
and the matching of ammunition to chamber.
Still, rimfire enthusiasts are not
without any means of ammunition quality control. One of the newest of these tools is the
G3 Rimfire Thickness Gauge from Sinclair International of Fort Wayne, Indiana.
The name refers to the tools
ability to measure the thickness of the cartridge rim. There are two reasons for doing
this. First is that rimfire cartridges headspace on the rim and some guns seem to be more
accurate with a particular thickness. Second is that the priming compound in a rimfire
cartridge is distributed within the rim. Differing rim thicknesses could hold differing
amounts of the compound and, in turn, effect ignition and consequently, accuracy.
There are several tools available
that are designed to measure rim thickness. None seem to be any easier to use than this
one or any more accurate or any less expensive. This latter, in part, because it is
designed to be used in conjunction with another tool it is assumed we already have - a
caliper. Fair assumption, for if youre reading this, in this magazine, youve
most likely accumulated a few tools, including a caliper.
The Rimfire Thickness Gauge is made
of aluminum and is about 1 7/16 inches long. It vaguely resembles the neck, shoulder and
beginning of the body of a cartridge case. A cut in one end allows the tool to be affixed
to the movable jaw of a caliper and secured by a screw. The other end is open to receive a
cartridge. The tools use is restricted to standard .22 fodder: .22 Short, Long and
Long Rifle and even CB and BB caps, if youre interested. It will not accept .22
Winchester Magnum ammunition or the older .22 WRF or .22 Remington Special. Attached to
the tool is a lanyard, designed to be slipped around the neck when the tool is being used.
Displaying the brilliance of simplicity, the lanyard can prevent the tool from being
dropped. As all rimfire fans know, it is percussion that fires the round, whether in the
chamber or in a tool such as this dropped on a hard surface. As the instructions note:
The neck you save may be your own!! Or, I might add, some one elses.
Regardless, the gauge is simple and safe to use, and made even safer with the lanyard.
According to Sinclairs
literature, the tool is designed to be used with a digital or dial caliper. Actually it
can be used with a vernier caliper as well. The difference is in ease of use and, perhaps,
a slight loss of accuracy when a vernier style is employed. When the gauge is affixed to
the movable jaw of a digital or dial caliper and the jaws closed on the empty tool, the
caliper can generally be zeroed, allowing measurements taken with a cartridge in place to
be absolute. With a vernier caliper, no zeroing can take place. Instead, the empty
reading must be recorded as a base and each subsequent measurement with a cartridge in
place recorded and the difference determined to arrive at an absolute thickness. In
practice, this can often be done in ones head, or ignored, simply using the
measurement with a cartridge in place. Those with the same measurement get sorted, and
Using the Rimfire Thickness Gauge is
dirt simple. Justifying its use is another matter. For most of us, with our
over-the-counter guns with their over-the-counter chambers, shooting whatever .22
ammunition is on hand is just fine. We get our offhand practice, plinking or small game
hunting and were happy. Theres certainly nothing wrong with that. Some of us,
though, go to the trouble of determining which brand of ammunition seems to be the most
accurate in our gun and only use that brand. This thoroughly practical approach is
sometimes expanded upon to find a single lot of one brand that is most accurate
and then buy as much of it as we
can. We then reserve the use of that ammunition for that particular gun. I recently took
this approach with a new .22 pistol for which I had high hopes. It took awhile, but I
finally found a particular brand and lot of ammunition that met my demands. I quickly
bought a case of it.
Some of us take all this even
farther and enter the competitive arena. Bullseye, silhouette and bench- rest competitions abound for the
rimfire addict. Benchrest shooters compete under BR-50 International sanction. No
off-the-shelf stuff here. Custom rifles with custom barrels and custom, match chambers are
the norm. Ammunition is often tested, weighed, measured and sorted until each round in
each group is as alike as is possible. Measuring rim thickness is part of the game.
Others who might be attracted to
tools such as these are folks like me who would like to quantify those qualities that make
some ammunition more accurate than others. For example, in comparing a half-dozen brands
on hand recently, I found several things of interest. The most accurate ammunition was the
most expensive, although no where near the $10 to $12 per box being charged for
top-of-the-line ammo these days. It had the thinnest rim thickness, averaging .034 to .035
inch compared to the .037 to .040 inch of others; it had the smallest extreme spread in
rim thickness, .002 inch compared to the .003 to .004 inch of others. The most accurate
ammunition also had the smallest extreme spread in cartridge weight, .3 grain over a box
of 50, with the vast majority within .2 grain, compared to .4 to .5 grain differences in
other brands. I also found the most accurate ammunition to be very slightly larger in
diameter, perhaps offering a better fit in over-the-counter chambers.
All this came from measuring and sorting and
shooting. Most of us already have the tools: a scale, a micrometer and a caliper. Add the
G3 Rimfire Thickness Gauge and were in business. When sorting cartridges we need a
block to hold the individual rounds, much like the loading blocks reloaders use, except
sized to hold .22 ammunition. Sinclair has these too, along with a host of other items for
the precision minded. The company can be reached at 2330 Wayne Haven St., Fort Wayne IN
46803; www.sinclairintl.com; or by e-mail: email@example.com. - R.H. VanDenburg, Jr.