Barrels for arms of the first class shall not be qualified for proof until they shall be in a fit and proper state for setting up. Barrels for arms of the third class shall not be qualified for proof until they shall be in a fit and proper state for setting up, with the proper breeches in; and all barrels lumped for percussioning shall be proved through the nipple hole, with the proper pins or plugs in. Barrels for arms of the second and fourth classes: For provisional proof:--If of plain metal, shall be bored and ground, having plugs attached, with touch-holes drilled in the plugs, of a diameter not exceeding one-sixteenth of an inch. If any touch-hole shall be enlarged, from any cause whatever, to a dimension exceeding in diameter one-tenth of an inch, the barrel shall be disqualified for proof. Notches in the plugs instead of drilled touch-holes shall disqualify for proof. If of twisted metal, they shall be fine-bored, and struck up, with proving plugs attached, and touch-holes drilled as in the case of plain metal barrels. For definitive proof:--The barrels, whether of plain or twisted metal, shall be in the finished state, ready for setting up, with the breeches in the percussioned state, break-offs fitted and locks jointed; the top and bottom ribs shall be rough struck up, pipes, loops, and stoppers on. All rifle barrels must be rifled; the top and bottom ribs of double barrels shall be struck up, pipes, loops, and stoppers on, the proper breeches in, and the thread of the screws shall be sufficiently sound and full for proof. Barrels for revolving arms of the fifth class shall have the cylinders with the revolving action attached and complete. Barrels for breech-loading arms of the fifth class shall be subject to provisional proof, according to the class to which they belong, and to definitive proof when the breech-loading action is attached and complete. _Marks of Proof._ The marks applicable to the definitive proof shall be the proof and view marks now used by the two companies respectively. The marks applicable to the provisional proof for the Gunmakers Company shall be the letters (G.P.) interlaced in a cypher surmounted by a lion rampant, and for the Birmingham Company shall be the letters (B.P.) interlaced in a cypher surmounted by a Crown. [Illustration: London marks.] [Illustration: Birmingham marks.] _Mode of affixing Proof Marks._ On arms of the first and third classes the definitive proof mark and view mark shall be impressed at the breech end of the barrel, and if the barrel be constructed with a patent breech, the view mark shall be also impressed upon the breech.