[Unclenick]

The current SAAMI drawing shows the 45-70 cartridge with a 1.44° included angle taper. However, the CIP has the taper at half that. I am inclined to think the SAAMI taper could be an updated design for improving lever gun feeding. A trapdoor action, after all, can even handle a reverse taper.

Also, just to be pedantic, a symmetrically tapered cylinder that doesn't come to a point is not a cone but a conical frustum, meaning forming a cone was frustrated by falling short of including the pointed tip.

1972Redneck, if you take a large capacity bottleneck case and make it straight, it gets very long and, assuming matching wall thickness, it gets heavier than the bottleneck case that holds the same powder charge as the surface area to volume ratio is getting bigger with a long, skinny case. Efficient use of volume is important to carry weight and packing efficiency, as is the ease of feeding from a magazine. That last point means the designer is not having to require a bolt to be impractically long and heavy in a modern rifle chambered for the same round. Moreover, powder burns less efficiently in a long, tall case as the flame front has to travel further to get from the rear to the front of the powder column. Finally, for a given exterior barrel length, a long cartridge gets less rifled barrel length than its shorter counterpart, so a little velocity is sacrificed by using one.