Brownells - Jack Rowe, Master Gunsmith Series, Bore Size and Proofing, Part 1 of 6

Published on May 30, 2012
Duration: 8:28

This video demonstrates how a master gunsmith uses a specialized bore gauge to measure the internal diameter of shotgun barrels at a specific point (9 inches from the breech face). It emphasizes the importance of checking bore size and wall thickness for safety and legal compliance, particularly in regions with proofing laws. The instructor also explains how to interpret proof marks and their historical context, highlighting the differences in regulations between the UK/Europe and the US.

Quick Summary

Master Gunsmith Jack Rowe explains how to measure shotgun bore sizes using a specialized gauge, typically at 9 inches from the breech. He emphasizes checking barrel wall thickness and interpreting proof marks, noting that in the US, there are no mandatory proofing laws, unlike in Europe where selling out-of-proof firearms is illegal.

Chapters

  1. 00:08Introduction to Bore Size and Wall Thickness
  2. 01:04Using a Bore Gauge
  3. 01:31Setting Up the Bore Gauge
  4. 02:30Measuring 12 Gauge Barrels
  5. 03:27Checking Proof Marks
  6. 03:50Metric Proof Size Conversion
  7. 04:41Barrel Tolerance and Out of Proof
  8. 05:08Proof Rules and US vs. Europe
  9. 06:10Different Rules of Proof
  10. 07:30Legal Ramifications of Out of Proof Firearms
  11. 08:00Pre-1989 Barrel Markings

Frequently Asked Questions

How do you measure the bore size of a shotgun barrel?

You use a specialized bore gauge with interchangeable heads. After calibrating it to zero with a known-size tube, you insert it into the barrel and measure the diameter at a specific point, typically 9 inches from the breech face, reading the measurement on the gauge.

What are proof marks on a firearm barrel?

Proof marks are stamps indicating that a firearm barrel has undergone rigorous pressure testing to ensure it can withstand normal operating pressures. They also often denote the original bore size and the specific proof rules under which it was tested.

What is the acceptable tolerance for barrel enlargement in proofed firearms?

Tolerances vary by proof rules. For example, under older rules, a barrel might be considered out of proof if its bore enlarged by more than .008 inches. Under the 1954 rules, up to .010 inches of enlargement was permissible.

Are there proofing laws in the United States?

No, the United States does not have national proof houses or mandatory proof rules like many European countries. This means firearms can be sold without the same level of mandated safety testing regarding barrel integrity.

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