The bore of the barrel, at the muzzle end
shall be concentric with barrel outside diameter within 0.015
The barrel shall be a commercial 20-inch barrel, unless
other length is required (see Table I and 6.2), except that the
protective finish shall be in accordance with 3.10.13. The
barrel wall thickness at the muzzle shall be .095 inches minimum.
The wall thickness at any other place along the barrel length
shall be equal to or greater than the thickness at the muzzle
end. The barrel chamber shall be in accordance with ANSI B46.1,
and have a surface finish of 63 microinches RMS or smoother.
3.8.1 Barrel Type III. The barrel for Type III shotguns
shall be fitted with rifle type front and open rear sight. The
rear sight shall be adjustable for both windage and elevation.
It shall contain positive locking devices which preclude
inadvertent misadjustment due to recoil or rough handling.
3.9 Sling swivel assemblv.
Shotguns shall be
3.9.1 Butt stock sling swivel assemblv.
equipped with a butt stock sling swivel assembly conforming to
Drawing 6147721, and shall be attached to the butt stock in
accordance with Figure 1. There shall be no relative movement of
the swivel plate. After assembly, the sling swivel shall swivel
freely 180 degrees.
3.9.2 Commercially equivalent hardware. Commercially
equivalent hardware may be substituted for the butt stock sling
swivel assembly provided it can sustain a 220-pound load applied
perpendicular to the stock line without separation.
3.9.3 Front sling swivel. Shotguns shall be equipped with
a front sling swivel on or forward of the barrel takedown mount
that will accept the shotgun sling and be acceptable to the
procuring activity. Load requirement is identical to 3.9.2.
The general characteristics
3.10 General characteristics.
of Type I, Type II and Type III shotguns shall be in accordance
with Table I.