Bench 4

Priming

Seat one primer lot consistently so ignition starts from a safe, repeatable, below-flush condition.

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Bench 4 Safety
Priming
!
Keep primers away from powder

Primers contain impact-sensitive compound. Prime cases as a separate operation before powder charging begins. Keep loose powder off the bench while primers are being seated, and keep primer trays, primer tubes, and priming tools away from open powder containers.

!
Use the tool's primer feed system

Do not pour primers into your hand or work from a loose pile on the bench. Keep primers in their factory packaging until you are ready to prime, then load them through the priming tool's intended feed system. Depending on the tool, that may be a hand-primer tray, bench-primer tray, primer strip, pickup tube, magazine tube, or press-mounted feed. Follow the tool instructions and stop if a primer jams or requires force.

Note The correct primer feed setup for your tool
Bench 4 Basics
Priming
What you're doing and why
Bench 4 turns prepared brass into primed brass. The pocket work should already be prepped at Bench 2. Here the job is to keep one primer type and lot together, seat each primer with firm, controlled pressure, feel for abnormally high or low resistance, and document your results.
1
Inspect the primer pocket

Bench 4 starts with primer pockets that should already be cleaned, inspected, and prepped at Bench 2. Before seating a primer, confirm the pocket is open, free of media or brass chips, and ready to accept a primer without obstruction. Do not force a primer into a dirty, obstructed, crimped, or damaged pocket.

You'll need Prepared brass from Bench 2 + visual inspection
2
Feel for pocket tension

Primer pockets loosen as brass is fired and reused. During seating, pay attention to resistance. A normal pocket gives steady, controlled resistance as the primer seats. A pocket that accepts the primer with little or no resistance is telling you the case may be at end of life. Pull loose-pocket cases from the batch.

You'll need Hand priming tool, bench priming tool, or press-mounted priming system and prepped brass
3
Seat below flush

Seat each primer squarely into the pocket until it is below the case head, commonly around 0.003" to 0.008" below flush. Use firm, controlled pressure, not force. A high primer is a safety issue and must not move forward. If a primer stops early or feels wrong, stop and investigate before the case continues.

Bench 4 Control
Priming
What you're controlling
Bench 4 controls primer identity and primer-pocket consistency. Sigma8 does not treat primer seating depth as a normal measured load-development variable. The practical control is to keep primer brand, type, and lot fixed inside the batch, maintain consistent primer pockets, and document any seating behavior that signals a pocket or brass-life problem.
C1
Primer Identity
Keep primer identity fixed

Primer brand, primer type, and lot number are part of the load record. Do not mix primer brands, types, or lot numbers inside one load-development batch. If the primer lot changes later, record it as a batch change, not the same exact recipe.

You'll need Primer lot number record
C2
Primer Pocket
Control the primer pocket

Primer seating starts with the pocket. This is why Sigma8 recommends uniforming primer pockets at least once, then making light periodic passes with the uniforming tool every 2-3 firings to maintain consistent pocket bottoms across the batch. The goal is not to turn Bench 4 into a primer-depth measuring exercise. The goal is to make the pocket consistent before the primer is seated.

You'll need Primer pocket uniformer
Logbook Record Layer

- Primer brand, type, and lot number
- Primer-pocket uniforming status and any periodic pass performed
- Cases that seat unusually loose, unusually tight, or otherwise feel wrong
- Cases pulled from the batch and the reason: loose pocket, high resistance, obstruction, damaged pocket, or other abnormal seating behavior
- Date and Qual8 session number

Bench walkthrough
Watch the bench in practice
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Bench 4
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Priming walkthrough — primer pocket prep, seating depth, and primer selection
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