The unique feature of this patent is stated, starting at the bottom of of column seven. It consists of a novel heat treatment of the plain, low carbon steels in order to provide improved case properties. This patent is highly detailed. Most of the information covers the normal annealing and cold working of the case material, and all of the almost trivial details of lubrication and cleaning. The patentees add a temper and heat treat that apparently is not normally used, probably because the 1015 and 1030 steels are not considered to be heat treatable due to their low carbon contents(0.15% and 0.30% respectively). The carbon level for heat hardening steels is considered to start at about 0.50 %.
Something that is not clearly stated in this patent, is the type of steel normally used in steel cartridge case fabrication. In outside research earlier this winter, I found the recommended steel to be “Special Drawing Grade 1008 Steel” (0.08% carbon). I will try to cite my source on this later, as it will take some time to check my books. This steel is a “thoroughly killed and rimmed steel” which means special steps are taken to minimize the absorbtion of gases into the steel as the ingot is smelted and poured at the foundry, then removal of any flawed portion of the ingot before it is forged into a billet prior to cold rolling. The most troublesome flaws are piping, which are voids that occur as gases escape from the metal upon cooling, and shrink voids, formed by contraction upon cooling. These flaws are mostly confined to the upper end of the vertically cast ingot. This bad end is cut off, leading to a higher waste factor. All of this means that an expensive grade of low carbon steel is the norm for cartridge cases. It would appear, although it is not clearly stated in this patent, that the authors are also using a lower than typical cost material in the form of regular cold rolled 1015 and 1030 steel. I don’t know if “Special Drawing” grades of these steels are available.
I don’t know what the normal failure rates for brass or steel cartridges are, but the number of ruptures listed in the testing section seems rather high, even though they appear to be bragged about. Maybe steel cases are actually more problematic in use than I have been lead to believe.
Thank You Enfield56 for bringing this patent to my attention. It provides me with a wealth of details that I have been interested in. Curt Laws