Equipment Setup

Why the Micrometer on Your MatchMaster Does Not Read Zero

The number on the thimble is a reference for adjustment, not a measurement of case length. Here is how to work with it.

Why it reads that way

The micrometer assembly is engineered to be untimed. Nothing indexes the thimble graduations to a fixed starting position, so where the zero lands relative to the sleeve varies from unit to unit.

That means the number you see is a reference for adjustment rather than an absolute reading of case length. A replacement micrometer would land somewhere of its own and work exactly the same way. There is nothing to correct.

What this is not

An offset thimble is not a defect and it does not affect the accuracy of the cut. The micrometer controls how far the cutter travels. It does not measure the case, and it was never intended to align to zero at any particular setting.

How to use it as a reference

Read the micrometer for movement, not for position. Each graduation on the thimble represents .001" of cutter travel, so what matters is how far you turn it from a point you established yourself.

Establish your reference point

Insert an untrimmed case in the case holder and bring it into contact with the cutter. Back the micrometer out until it contacts the micrometer stop on the carriage, and note whatever it reads. That number is your starting point for this setup.

Close up of the MatchMaster micrometer with the untrimmed case in contact with the cutter, the thimble reading between the 15 and 25 graduations. — Untrimmed case in the case holder and in contact with the cutter, micrometer backed out until it contacts the stop on the carriage. On this unit the reference point falls at .020 rather than at zero.

Count the travel, not the number

To remove material, turn the micrometer that many thousandths away from your reference point. Twenty graduations of travel removes .020" from the case, and it does that identically whether your reference sat at .020 or anywhere else on the dial.

Close up of the MatchMaster micrometer after twenty graduations of travel, the thimble now reading zero. — The same micrometer after twenty graduations of travel from the reference point above. The .020 shown here illustrates how the graduations track cutter movement. It is not a recommended amount to take off a case.

Confirm with calipers

Trim one case, measure it, and compare against the trim-to length published for your cartridge. Adjust from your reference point and check again. Two or three cases is usually enough to land on the setting.

Write the reference down

Once you have the trimmer set for a cartridge, record the micrometer reading along with the pilot and case holder you used. Returning to that number gets you back to the same cut without starting over.

Do not try to force it to zero

There is no adjustment intended to bring the thimble zero into alignment with the sleeve, and attempting to make one will not improve how the trimmer cuts. Treat the reading as relative and it will serve you the same way a zeroed one would.

The short version

The micrometer assembly is not timed, so the thimble zero will not necessarily align with the sleeve.
The reading is a reference for adjustment, not a measurement of case length.
Each graduation is .001" of cutter travel. Count from your own reference point.
Verify with calipers and record the setting for next time.

MatchMaster Precision Case Trimmer

Micrometer adjustment, a self-centering collet, and repeatable case length, cut after cut.

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