I believe it is a Laminated Steel variant, not typically seen that late
https://docs.google.com/document/edit?id=1__gn3XKjLX_4V0LguzoVGBwJRFS6SxsWGzUwHq93neoThe Gun and Its Development, W.W. Greener, 8th edition, 1907
http://books.google.com/books?id=3HMCAAAAYAAJ&pg=PA224&dq"In the foregoing descriptions of the methods of manufacturing twist barrels it is stated incidentally that some kinds are superior to others. The comparative strength of gun barrels and of the material employed in their manufacture, the merits and disadvantages of chosen varieties, will be found stated in detail later, but as the method of manufacture, as well as the material employed, affect the quality of the barrel, it is advisable to state here that, so far as known, the strongest forged or twist barrel is the laminated steel now usually termed "stub-Damascus," made of three twisted rods to the riband.
The word laminated, as the designation of a gun barrel, arose from the fact that early in the last century thin strips, plates, or lamina of steel, piled alternately with iron strips or plates, formed the composite metal from which they were made. They differ from Damascus in so far as the iron and steel are differently arranged in the pile, so that instead of a decided curl in the figure there is only what may be termed "
herring-bone" lines running spirally round the barrel from end to end."
John Henry Walsh referred to this as "
angularly laminated."
