Handloading PART VI, How to Measure Cartridge Overall Length ~ GunBlue's Complete Guide

Published on March 4, 2016
Duration: 38:10

This guide details a cost-effective DIY method for measuring Cartridge Overall Length (COAL) using common tools like scotch tape and dial calipers, bypassing expensive commercial gauges. It explains COAL's importance for safety and accuracy, referencing SAAMI standards and reloading manuals. The video emphasizes understanding factors limiting COAL, such as magazine capacity and bullet design, and provides a practical, step-by-step process for determining maximum COAL specific to a rifle and bullet combination.

Quick Summary

Measure Cartridge Overall Length (COAL) accurately using a DIY method with scotch tape and dial calipers. This technique bypasses expensive tools and helps determine safe, accurate seating depths by measuring the distance from the bolt face to the rifling.

Chapters

  1. 00:00Intro: DIY COAL Measurement
  2. 01:00Understanding COAL Standards & SAAMI
  3. 03:38Factors Limiting COAL (Magazine Capacity)
  4. 07:30Cardinal Rule: Bullet Seating Depth
  5. 10:00Bullet Jump & Accuracy Explained
  6. 13:55Step-by-Step DIY COAL Measurement Process
  7. 15:54Calculating Maximum COAL & Working Loads

Frequently Asked Questions

What is Cartridge Overall Length (COAL) and why is it important?

COAL is the measurement from the cartridge base to the bullet tip. It's crucial for ensuring cartridges fit magazines and chambers safely, and it directly impacts chamber pressure and accuracy. SAAMI sets standards for commercial ammo.

How can I measure COAL without expensive tools?

You can use a simple DIY method with scotch tape and dial calipers. Mark a cleaning rod at the muzzle after seating a bullet against the rifling, then mark it again at the bolt face. The distance between these marks, minus desired bullet jump, gives your working COAL.

What factors limit the maximum COAL for a rifle cartridge?

The primary limiting factor is often the firearm's magazine capacity, which dictates the maximum length a cartridge can be and still feed reliably. Bullet design, like boat tails, can also affect internal case capacity.

What is the optimal 'bullet jump' for accuracy?

Optimal accuracy is typically achieved when the bullet has a slight 'jump' to the rifling, usually between 0.015 and 0.030 inches. This allows the bullet to gain momentum before engaging the rifling, preventing pressure spikes.

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