MIL-DTL-13931J
applicable drawings and specifications. When specified, the tube interior surfaces shall be magnetic-
particle inspected with a black-light borescope in accordance with applicable drawings and specifications.
4.5.8 Rifling operation. The rifling of the first weapon furnished under a contract shall be witnessed by
the Government representative (see 6.4.1), who shall observe the operation and verify any measurement
or detail necessary. Subsequent rifling operations shall be subject to periodic check by the Government
representative for verifying that the contractor's control of the process provides adequate assurance of
conformance to the drawing requirements.
4.5.9 Inspection of bore surfaces. Areas sufficiently near the muzzle or breech shall be checked by direct
comparison with the applicable surface roughness specimens. The remaining surfaces shall be checked
with a borescope by comparison with the surface previously compared to the specimens.
4.5.10 Bore and chamber diameter gaging.
4.5.10.1 Preparation for gaging . Preparation for gaging shall be meticulous to assure accuracy. The
chamber and the bore shall be dry and free of all foreign material. During inclement weather gaging shall
be performed under cover.
4.5.10.2 Method of inspection. Bore and chamber measurements shall be taken with a star gage, an air
gage, an electronic gage, or approved equivalent inspection equipment.
4.5.10.3 Measuring tube bores. For rifled cannon, all bore measurements made in a tube shall be
located relative to the "vertical land", which is defined as the land at the six o'clock position at the
commencement of rifling location when the cannon is in a normal (as mounted) position. The adjacent
groove in a clockwise rotation, as one faces the muzzle, is designated the "vertical groove". Due to
various rifling lengths/bore diameters/rifling twists, the correct land and groove "clocking" position for
application of the stargage at muzzle end must be computed for each model cannon; such that upon full
insertion, a measuring device probe tip will align with the vertical land/groove at the commencement of
rifling location.
4.5.10.4 Gaging tapered areas in chambers. Tapered areas less than 0.125 inch per inch and with an
axial length greater than 0.5 inch shall be measured in two series of 0.5 inch intervals, 90 degrees apart,
to verify conformance to the taper requirements. Readings shall be recorded and evaluated as variations
from a basic cone with a 0.005 inch variation as the maximum permissible. Maximum diameters are not
to exceed drawing requirements. Chamber gages may be used in other than the above areas to verify
conformance to specified requirements (see 4.5.10.2).
4.5.10.5 Record of measurement. The contractor's record of final measurements of bore and chamber
shall accompany each tube.
4.5.11 Wall thickness. The following shall be the minimum acceptable procedures for determining tube
wall thickness variations.
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