W W Greener discussed the sharp forcing cones in his works. I do not know where it first occurred but he included it in his "The gun & its Development", 1910 edition. It was according to him an attempt to do away with the possibility of gas leakage while the load passed through the cone. He Strongly Condemned the practice, recommending the ordinary cone. A word of caution if you have a gun so chambered; "DO NOT" fire it with a shell longer than the chamber. At this point in time, all paper shells were closed with the roll crimp. One should Never fire a shell in which the end of the fired shell laps into the bore itself.
My ca 1913 LAC catalog lists loads in 12 gauge of up to 3½ drams, or equivalent, of powder behind 1¼ oz of shot. Those aren't weak even by modern standards. This includes a measured amount of Black or Bulk Smokeless & up to 28 grains of Ballistite or Infallible (same composition as Unique only slightly thinner flakes, thus a bit faster). You will not find a load today listing as much as 28 grains of Unique pushing 1¼ oz of shot.
From Drew's pictures, it appears that perhaps Tobin copied the Lefever design, except he changed the bolting. Can't really tell from the pictures how closely he followed Alexander Brown's original rotary bolt design. Brown's intent was that his bolt should serve two purposes, 1st hold the barrels down & 2nd hold the standing breech up to the barrel breech. It can accomplish both purposes only with precise fitting & usually the secondary function suffers.
Lefever accomplished the two purposes by using a square-shouldered "Doll's Head" & then a wedge bolt working in the rear of the Doll's Head. All of the ones I have had seem to have been extremely well fitted & served both functions well.
I would have no fear of "Action Strength" in my Lefevers even with modern short Magnums, but keep my loads light in respect to barrel strength & 100+-year-old wood.
