minimum breech diameter for shotgun

Discussion in 'Gunsmithing Forum' started by mattybock, Apr 7, 2014.

  1. mattybock

    mattybock New Member

    So far, as much as I can gather, the minimum breech diameter of the barrel of a rifle should be the width of the base of the cartridge multiplied by 1.8.
    But this does not seem to be the case with shotguns, as black powder fowler barrels of .62 caliber/20 bore seem to have walls that are only 1/3rd the thickness of the internal diameter of the breech.
    My own black powder rifle has a breech at around 1.5 to 2xs the diameter of the bore. The barrel is not a true cylinder, but octagon in shape.

    So this leaves me with mixed messages.
    What is the minimum safe outside diameter of the breech end of a modern smokeless shotgun barrel in relation to the bore diameter?
  2. c3shooter

    c3shooter Administrator Staff Member

    Attempting to compare shotguns and rifles is similar to comparing lightning bugs and lightning. Not only do they operate at totally different pressures, but the pressure curve is different.

    12 g- 11,500 PSI

    308 Winchester- 62,000 psi

    Perhaps your best measure would be to remove the barrel from a pump gun, such as the Mossberg 500 or Ithaca 37, and measure it. Very small bore shotguns, such as the .410 will have proportionally thicker chambers and barrels- not for internal pressures, but to withstand external abuses.

  3. hiwall

    hiwall Well-Known Member

    Also commonly European made guns have thinner barrels than US made guns(they often use different steel).
  4. robocop10mm

    robocop10mm Lifetime Supporting Member Lifetime Supporter

    It does certainly depend on the steel used. High quality steel can be thinner and still be as strong.