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ACCESSORY REVIEW,
February 2001:


Mitutoyo Digimatic "MyCal" Caliper

 
Crufflers like to measure things.  Moreover, we like to measure things with a startling degree of accuracy.  It's not enough for us to say that the barrel on a Mauser Gewehr 98 is 29 inches long.  No, we have to know, say, and write that the barrel is actually 29.13 inches in length.  We habitually measure headspace down 
Mitutoyo MyCal Digimatic Caliper
to the thousandth of an inch.  Bore diameters are typically discussed in hundredths of a millimeter.  Now before you run off screaming about cruffling creating a caste of myopic, minutiae oriented, anal retentive cretins, remember that tiny dimensional deviations do matter.  The difference between a dangerous rifle or a serviceable one is often a matter of a few thousandths of an inch in the headspace dimension.  Likewise, precision shooting requires the utmost in repeatability.  The exact diameter of a bullet or bore and the exact length of a case are critical dimensions for accuracy.

Why Calipers?
There are a couple of types of tools one can use to rapidly and accurately determine dimensions to within a thousandth of an inch or better.  Among these are the micrometer and the caliper.  The micrometer is not frequently used.  Although it is extremely accurate, the micrometer often has a very limited range over which it can be used - almost always less than two inches.  As a result the caliper is generally the tool of choice when a device to measure distances of up to six or eight inches is required.

Vernier, Dial, or Digital
Typically, calipers are available in three variations:  vernier, dial, and digital.  Vernier calipers indicate measurement by means of a sliding scale, not unlike a slide rule.  Dial calipers indicate measurement on a dial gauge (think of an analog tachometer or speedometer).  Digital calipers indicate the measurement on a digital readout, usually using an integral LCD display.  With respect to expense, vernier calipers are by far the least expensive, with quality dial and digital calipers running neck and neck.  Digital calipers typically cost a few dollars more than comparable dial calipers.

The small additional cost of a digital caliper is offset by the versatility and ease of use.  Most digital calipers switch between imperial and metric measurements at the touch of a button.  And there's no need to learn to "read" a digital caliper - the results of your measurement are immediately read out on the LCD display.  Based on ease of use (and our own inherent laziness!), we decided to go with a digital caliper.

Going with Mitutoyo
Having opted for a digital caliper, our next step was to determine which brand to purchase.  Some quick initial research narrowed our choices down to five brands, Mitutoyo, Starrett, Mahr, Brown & Sharpe, and Fowler.  All of the manufacturers made at least one six inch caliper model that had a resolution of .0005", with an accuracy of .001".  All save the Fowler offered both inside and outside diameter measurement capability.  Several, the Fowler, the Starrett, and the Mahr, offered output to a serial cable (RS-232) for connection to a PC or other measuring system.  After researching each of the companies, and gauging the various product capabilities, we decided to go with the Mitutoyo product, as this offered the best compromise between price and capability.  While a serial output would have been nice, we could think of no realistic use for this functionality.  Prices for six inch calipers from Enco ran from $94.00 for the Mitutoyo "MyCal" to $131.25 for the Brown & Sharpe "Digit-Cal Mark IV."   We ordered the Mitutoyo. (Mitutoyo, which, incidentally, is the world's largest metrology company, was founded in 1934, producing mechanical micrometers.)
 

Physical Characteristics
The caliper arrived a few days later.  It was packaged in a fitted plastic box along with the instructions and the battery.  The battery, an SR-44 type available at most consumer electronic stores, was packaged in a sealed plastic capsule affixed to the instructions.  The caliper itself is nicely executed in stainless steel, with the graduated scale on the front.  The scale also contains the printed circuit that interacts with the readout on the slide.  The slide has a thumbwheel for ease of manipulation, and a large readout display.  There are four buttons around the display:  A power switch, a toggle between zero and absolute measurements, an origin set, and an inch/millimeter toggle.  There is a set screw atop the slide which may be used to hold it at a given position.

To ready the caliper for use, open the battery compartment, and seat the battery.  Then depress the power button for a moment.  It is unlikely that the readout will indicate that the closed position is the origin point.  Slide the caliper to the fully closed position and hold the Origin button down for approximately two seconds.  This will set the closed position as the zero point.  At this point, you're ready to measure.
 

Field Test
The object of our field test was to determine the caliper's ease of use on various cruffling related items, as well as the measurement's accuracy and repeatability.  To this end we assembled the following measurement candidates:

Each set of ammunition was measured for bullet diameter and case length.  Headspace gauges were measured for rim thickness.  The measurements were repeated three times to verify caliper resolution and consistency.  The results are noted below.
 
Federal Hydra-Shok 9x19mm Ammunition 
 
Measurement Set One
Measurement Set Two
Measurement Set Three
 
Bullet Diameter
Case Length
Bullet Diameter
Case Length
Bullet Diameter
Case Length
Round 1
0.3540"
0.7495"
0.3540"
0.7495"
0.3540"
0.7495"
Round 2
0.3535"
0.7510"
0.3535"
0.7510"
0.3535"
0.7510"
Round 3
0.3540"
0.7480"
0.3540"
0.7480"
0.3540"
0.7480"
Round 4
0.3540"
0.7480"
0.3540"
0.7480"
0.3540"
0.7480"
Round 5
0.3535"
0.7480"
0.3535"
0.7480"
0.3535"
0.7480"
No deviation in caliper measurement noted.



 
 
 
 
 
 
 
 
Czech Military 7.62x25mm Ammunition
 
Measurement Set One
Measurement Set Two
Measurement Set Three
 
Bullet Diameter
Case Length
Bullet Diameter
Case Length
Bullet Diameter
Case Length
Round 1
0.3060"
0.9720"
0.3060"
0.9720"
0.3060"
0.9720"
Round 2
0.3060"
0.9760"
0.3060"
0.9760"
0.3060"
0.9760"
Round 3
0.3065"
0.9760"
0.3060"
0.9760"
0.3060"
0.9760"
Round 4
0.3060"
0.9760"
0.3060"
0.9760"
0.3060"
0.9760"
Round 5
0.3060"
0.9760"
0.3060"
0.9760"
0.3060"
0.9760"

One deviation in caliper measurement noted - Round 3, bullet diameter fluctuation of 0.0005" between Measurement Sets One and Two.


Turkish Military 7.92x57mm Ammunition
 
Measurement Set One
Measurement Set Two
Measurement Set Three
 
Bullet Diameter
Case Length
Bullet Diameter
Case Length
Bullet Diameter
Case Length
Round 1
0.3220"
2.2420"
0.3220"
2.2420"
0.3220"
2.2420"
Round 2
0.3220"
2.2430"
0.3220"
2.2430"
0.3220"
2.2430"
Round 3
0.3215"
2.2420"
0.3215"
2.2420"
0.3215"
2.2420"
Round 4
0.3210"
2.2420"
0.3210"
2.2420"
0.3210"
2.2420"
Round 5
0.3215"
2.2410"
0.3215"
2.2410"
0.3215"
2.2410"

No deviation in caliper measurement noted.


South African 5.56x45mm Ammunition
 
Measurement Set One
Measurement Set Two
Measurement Set Three
 
Bullet Diameter
Case Length
Bullet Diameter
Case Length
Bullet Diameter
Case Length
Round 1
0.2235"
1.7530"
0.2235"
1.7530"
0.2235"
1.7530"
Round 2
0.2235"
1.7540"
0.2235"
1.7540"
0.2235"
1.7540"
Round 3
0.2235"
1.7540"
0.2235"
1.7540"
0.2235"
1.7540"
Round 4
0.2235"
1.7530"
0.2235"
1.7530"
0.2235"
1.7530"
Round 5
0.2235"
1.7545"
0.2235"
1.7545"
0.2235"
1.7545"

No deviation in caliper measurement noted.


Forster .303 British Headspace Gauges
 
Measurement  One
Measurement  Two
Measurement  Three
GO Gauge, Nominal .0640"
 0.0640"
 0.0640"
 0.0640"
NO-GO Gauge, Nominal .0670"
 0.0670"
 0.0670"
0.0670"
FIELD Gauge, Nominal .0700
 0.0700"
 0.0700"
 0.0700"

No deviation in caliper measurement noted.






Conclusion
Calipers are an important part of the cruffler's toolkit, and, if one reloads or does any sort of gunsmithing, indispensible.  Our tests and observations indicated that the MyCal was well calibrated and had an excellent consistency of measurement.  Moreover, the digital readout and controls were intuitive and easy to use.  That alone is an excellent recommendation - too often the application of technology to a relatively straight forward problem previously solved with mechanical means results in an overly  complex tool that is at best confusing.  By marrying technology and simplicity Mitutoyo has provided the best of all worlds for the hobbyist, cruffler, or anyone who needs a highly accurate but easily used measurement tool.  And let's not leave out price; at less than $100.00, the MyCal represents one of the best values in digital calipers out there.   While the Mitutoyo MyCal isn't the only good digital caliper available, it does represent one of the best compromises between price, capability, and ease of use.
 

And now, our Buy-O-Meter rating for the Mitutoyo MyCal digital caliper:
 

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