MIL-DTL-13931J
3.4.2.1.1 Straightening of tubes. Unless otherwise specified, cannon tubes may be cold-straightened to
reduce bends induced by machining, to comply with the limit of allowable bend specified on the finish
machined drawing, but not after final machining or rifling. (see 4.5.21 and Bend definition in 6.3.4).
Straightening shall be done at the option and risk of the machined tube contractor.
3.4.2.2 Breech recesses. Recesses in breech structures for housing breechblocks or supporting
obturating parts, and other recesses requiring resistance to firing pressure shall be free from scratches,
visible steps, scores or nicks.
3.4.3 Autofrettaged cannon tubes. When autofrettage (see 6.3) is specified for cannon tubes, approval of
the procedure to be used shall be obtained from the responsible Government design activity before the
start of operation.
3.4.4 Joining processes.
3.4.4.1 Welding. Welding is only permitted as specified on applicable engineering drawings unless
written approval is obtained from the Procuring Contracting Officer and the government design activity.
The welding terms and symbols used on the drawings shall be in accordance with AWS A2.4 and AWS
A3.0. The preparations for welding specified on a drawing may be modified subject to approval of the
responsible Government design activity. Weldments that are not machined after welding shall not be
distorted beyond the dimensional limits specified on the individual part detail drawings or weldment
drawing. Spatter and similar excess shall be removed. Unless otherwise specified on the drawing,
contours of deposited metal in joints shall not be altered.
3.4.4.2 Riveting. Wherever practical, rivets shall be machine driven and by a pressure method rather
than by impact. The rivets shall completely fill the holes, effect firm contact between the joined surfaces
and shall have full formed heads concentric with the body. Steel rivets over 3/16 inch in diameter shall be
driven hot; 3/16 inch and smaller in diameter may be driven cold. Nonferrous rivets shall be driven cold.
3.4.4.3 Staking. Staking (see 6.3.5) shall comply with the drawings.
3.4.5 Protective finishes.
3.4.5.1 Anodic coating. Anodic coatings shall comply with MIL-A-8625 or the applicable specification
shown on the drawing.
3.4.5.2 Chromium plating. When chromium plating is specified, the following shall apply:
3.4.5.2.1 Plating process. Prior to production plating, the contractor shall submit the details of the
plating process to be used to the Procuring Contracting Officer for approval by the responsible
Government design activity. The procedures shall include information on:
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