Brownells - Jack Rowe, Master Gunsmith Series, Bore Size and Proofing, Part 4 of 6

Published on May 30, 2012
Duration: 9:50

This video details the critical process of measuring shotgun barrel wall thickness, a key factor in determining a firearm's safety for modern proofing. Instructor Jack Rowe emphasizes a minimum acceptable thickness of 20,000ths of an inch, with 25,000ths being preferable. He also explains how to interpret proof marks, distinguishing between black powder and nitro proofing, and highlights historical practices that could lead to thinner barrels.

Quick Summary

Gunsmiths recommend a minimum shotgun barrel wall thickness of 20,000ths of an inch, with 25,000ths being ideal for safety with modern ammunition. Older guns may have thinner barrels due to historical balancing practices or lower black powder pressures.

Chapters

  1. 00:08Case Example: Burst Barrel
  2. 00:1628 Gauge Barrel Burst Incident
  3. 00:43Reloading and Liability
  4. 01:40Measuring Barrel Wall Thickness
  5. 02:07Setting Up the Measuring Tool
  6. 02:33Sliding Barrels onto the Gauge
  7. 02:51Reading Barrel Thickness
  8. 03:11Measurement Point: 9 Inches from Muzzle
  9. 04:07Acceptable Barrel Thickness (20,000ths)
  10. 04:36Modern Barrel Thickness (40,000ths)
  11. 04:47Consequences of Thin Barrels
  12. 05:13Historical Barrel Thinning Practices
  13. 05:42Black Powder vs. Nitro Powder Pressures
  14. 06:21Black Powder Burn Rate
  15. 06:06Nitro Powder Pressure Curve
  16. 06:34Smokeless Powder and Barrel Length
  17. 07:25Importance of Studying Proof Rules
  18. 07:31European Proof Marks
  19. 07:45Identifying Black Powder Guns
  20. 08:09Nitro Proof Mark Identification (NP)
  21. 08:34Old Markings (12 B 14 M)
  22. 09:05Choke Development and Ball Ammunition
  23. 09:32German Proof Marks

Frequently Asked Questions

What is the minimum acceptable wall thickness for shotgun barrels to be considered safe for modern proofing?

According to gunsmiths, a minimum acceptable wall thickness for shotgun barrels is generally considered to be 20,000ths of an inch. A thickness of 25,000ths is preferable for added safety margin when dealing with modern ammunition pressures.

How can I determine if an old English shotgun is safe for smokeless (nitro) ammunition?

Check the firearm's flats for specific proof marks. If an English gun lacks 'nitro proof' markings or the letters 'NP', it is likely only proven for black powder ammunition and should not be fired with smokeless loads.

Why were older shotgun barrels sometimes thinner than modern ones?

Historically, gun makers sometimes removed metal from barrels to achieve a desired balance before selling the firearm. Additionally, black powder, used in older firearms, generated lower pressures than modern nitro powders, allowing for thinner barrel construction.

Where is the most critical point to measure shotgun barrel wall thickness?

The most critical point to measure shotgun barrel wall thickness is typically at 9 inches from the muzzle. This location is a standard for assessing the barrel's integrity and its ability to withstand proofing pressures.

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