Another “might seem obvious to some, but not to me” post about how to “minimize the shoulders bump (I went for .002-.003), and the likely corresponding neck length growth … yep, it’s AI (Gemini specifically), but I followed it, and it worked, so posting here for the others in my boat (dense newbie)…
Here is the step-by-step process to set up your 31801 die: (RCBS 6CM FL sizer)
1. The Tooling Prep
To do this accurately, you cannot "eyeball" it. You need:
* Headspace Comparator: A tool that attaches to your calipers (like the Hornady Lock-N-Load).
* The Correct Bushing: For 6mm Creedmoor, use the .375" bushing (the same one used for 6.5 Creedmoor, as they share the same shoulder datum).
* 3–5 Fired Cases: These must be fired from your rifle and not resized yet.
2. Establish Your Baseline
* Measure 3–5 of your fired cases using the comparator.
* Average the readings. (Example: If they measure 1.524" at the shoulder datum, your target resized length is 1.522").
* Write this target number down.
3. Initial Die Placement
* Raise the press ram to the very top.
* Screw the sizer die into the press until it touches the shell holder.
* Back the die OUT (counter-clockwise) 1 full turn.
4. Apply a light coat of lube to one of your fired cases (don't forget the neck).
* Run the case into the die and back out. At this stage, it will only size the neck and won't touch the shoulder.
5. “Walking In" the Shoulder Bump. This is the "Precision Nudge" phase.
* Lower the Die: Loosen the lock ring and screw the die down (clockwise) in very small increments.
* Rule of Thumb: 1/8th of a turn is roughly .009". A tiny 5-degree nudge is roughly .001".
* Size and Measure: * Screw the die down about 1/4 turn from your starting point.
* Lube and size the case again.
* Measure with your comparator. If it still says 1.524", you haven't touched the shoulder yet.
* Fine Tuning: Continue lowering the die in 5-degree increments until you see the measurement drop.
* The Target: Once the comparator shows exactly .002" less than your starting average (e.g., 1.522"), you have found your setting.
6. See how they feed
* take four or five of the resize cases, and make sure they chamber in your rifle easily. If they do, go to the next step, if they don’t, you’re gonna need to bump the shoulder some more.
7. Final Lockdown
* With the case still inside the die and the ram at the top, tighten the die lock ring. (Having the case inside "centers" the die in the press threads for better alignment).
* Tighten the set screw on the lock ring.
* Verify: Take a new fired case and run it through. If it measures exactly at your target, you are perfectly set.
* Gap Check: Once set for a .002" bump, you will likely see a tiny visible gap between the bottom of the die and the shell holder when the ram is at the top. This is normal; it means you are no longer "over-sizing" to SAAMI minimums.
* Expander Ball Tension: Ensure your expander ball is lubed. If it's too dry, it can "pull" the shoulder back forward as you withdraw the case, ruining your .002" bump.
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