grayfox Wrote:DN I am coming to the same conclusion, about the unsupported brass, particularly with a Lapua/Odin combination setup. But to your post, I believe near to the base, the heat/temperature may be higher early in the ignition process but pressure, probably not. Pressure increase won't really occur until the entire volume of the case/bullet interior has that pressure increase. That might be some microseconds after the heat towards the base increases. But that heat can still have an impact on the brass down there, which will accelerate as the pressure (and deflagration) proceeds. Pressure buildup needs to have some gas generation, and pretty much the entire volume will see that pressure. Any local pressure beginnings in that ignition wave, will propagate forward, not build up in place down at the base.
grayfox I get what you are saying about pressure but I still think at the atomic and dynamic level there's going to be a gradient of it. The powder at the head end is going to burn first, thus the gas will form there first. The powder at the shoulder end is going to burn last. By this fact alone there is going to be a pressure difference. And I'm talking over a VERY short time interval. As you state the pressure overall in the case is going to get to an even expansion VERY quickly. Edit: And I'm not saying there's a "buildup" of it. I'm just saying that it will follow with literal burning of the powder that starts at the primer and that it simply follows alongside the formation of the gas and heat.
LOL I split hairs here with you, though. It doesn't matter in that the bottom line is that the case is going to expand the most where it is least supported...the feed cone area.