How ogive position, magazine length, throat geometry, and bullet design interact to produce predictable precision.

I. Why Seating Depth Matters in 6.5 Creedmoor

6.5 Creedmoor was engineered around long-for-caliber bullets (120–147 gr) with high-BC profiles. These bullets require controlled jump distance to achieve optimal stability and predictable vertical dispersion.

  • Long bearing surfaces
  • Modern secant or hybrid ogives
  • Magazine-fed COAL stability (~2.800″)
  • Low-pressure, consistent seating depth behavior

The result is a cartridge unusually tolerant of factory seating-depth variation.

II. COAL (Cartridge Overall Length) — Functional Boundaries

  • SAAMI max COAL: 2.825″
  • Magazine internal length: typically 2.830–2.850″
  • Throat/freebore: sized for heavy-for-caliber bullets seated with controlled jump
  • Factory match loads: optimized for consistent ogive-to-lands distance across chambers

Creedmoor does not require “touching the lands” to shoot well — its chamber blueprint rewards controlled jump.

III. Jump Distance — What Actually Happens

Ogive jump influences:

  • Initial pressure rise rate
  • Barrel time
  • Yaw behavior
  • Vertical dispersion

Typical optimal ranges:

  • 0.020–0.060″ jump for most high-BC bullets
  • Minimal BTO variation is more important than exact COAL
  • Jump-tuning yields modest ES/SD improvements

This is a core reason factory ELD-M loads earned their reputation for “plug-and-play” precision.

IV. Magazine Constraints & Why Creedmoor Solved the .260 Problem

.260 Remington’s problem:

  • Deep seating required to fit standard magazines
  • Reduced usable case capacity
  • Increased pressure
  • Greater velocity variation

Creedmoor’s solution:

  • Shorter case with a longer neck
  • Optimized throat for 140–147gr bullets
  • Better alignment for high-BC ogives

This is why Creedmoor became the dominant AR-10 precision cartridge.

V. Practical Accuracy Behavior

  • Factory ammunition: typically optimized for 0.030–0.050″ jump
  • Handloaders: often find broad, forgiving nodes (±0.003–0.005″)
  • Gas guns: prefer larger jump for reliability (0.050–0.070″)
  • Bolt guns: may show tight nodes around 0.015–0.035″

Creedmoor’s geometry allows consistent accuracy even with slight ogive variation from bullet to bullet.

Specifications

  • Technical Note: TN-03 — COAL, Jump & Seating Depth Dynamics
  • Compendium: 6.5 Creedmoor Cartridge Master Compendium
  • Focus: Ogive jump, COAL limits, magazine geometry, seating sensitivity
  • Related Topics: TN-01 Case Geometry, TN-02 Pressure Curve, TN-08 External Ballistics