MIL-DTL-13931J
c. The gas check seat surface shall not contain pits.
d. Pits are acceptable elsewhere on the chamber surfaces providing the size and density do not
exceed the criteria and thresholds designated by the design agency (see 6.2).
Any condition exceeding these criteria shall be reported as nonconforming material.
3.4.5.2.7 Visible plating defects after proof-firing. Unless otherwise specified by the specific cannon
specification, the following applies: After proof-firing, there shall be no defects in the gas check seat
zone. The remainder of the plated surface in a tube shall be free from any visible spalling depressions
(see 6.3.2) in excess of 4 inches cumulative length, and chipped areas (see 6.3.3) in excess of 16 inches
cumulative length.
3.4.5.2.7.1 Dimensional limits of spalling depressions. The overall length of a spalling depression in a
tube, measured parallel to the bore axis, shall not exceed two inches. The overall width of a spalling
depression, measured at right angles to the length, shall not exceed the criteria and thresholds designated
by the design agency (see 6.2).
3.4.5.2.7.2 Dimensional limits of chipped areas. The length of a chipped area in a tube, measured
parallel to the bore axis, shall not exceed four inches. The width, measured at right angles to the length,
shall not exceed the criteria and thresholds designated by the design agency (see 6.2). The length or width
is the distance between the outer edges of the outermost cavities.
3.4.5.3 Coating materials. Coating materials shall comply with the applicable engineering drawings, the
applicable specifications, and the following:
3.4.5.3.1 Mixing. Coating materials shall be prepared for application under clean conditions with clean
equipment. Materials shall be allowed to warm to room temperature before mixing. Skins, if present,
shall be carefully removed from the material. The materials shall be thoroughly stirred or shaken prior to
thinning and application. To avoid problems of incompatibility in the liquid and drying phases, mixing of
paints of the same specification but supplied by different manufacturers is prohibited. Every effort shall
be made to assure that a primer of a single manufacturer is used on the item to be finished and similarly
the top coat should be restricted to a product of a single manufacturer.
3.4.5.3.2 Selection of thinners. The thinner recommended on the package label or in the applicable
process specifications shall be employed. Other thinners as recommended by the paint manufacturer for
his particular product may be used.
3.4.5.3.3 Aged materials. Wash primers that are more than one year old from the date of manufacture,
primer paint that is more than two years old from the date of manufacture, and top coat paint that is past
the shelf life expiration date shall not be released for production use on exterior surfaces of cannon until
they have been subjected to all the inspection tests of the applicable material procurement specification,
including both the large scale panel spray tests and the scratch wet tape adhesion test specified in MIL-F-
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