I'm still processing the thread too. It's a great read that complements this thread. There's a pic of the cross section of Lapua, Starline, and Hornady brass and it confirms the same thing as the pic here - Hornady has the thicker base and overall more sidewall at the head than Lapua. Starline is in between like Norma was in the pic here.
Another thing is that Alexander himself pointed out again that the feed cone shape matters. And there are some supporting posts stating that some barrels (I think Odin) show more of a ring than others.
And I'm still not convinced that early bolt release matters. If you think about powder ignition, it's going to literally start burning right at the primer, right there at the head first. Pressure will be the highest there, relative to the shoulder end. And that pressure is going to expand the brass there at the head more than at the shoulder. And as the powder continues to burn there will be a high pressure front that moves with it and continue towards the shoulder. It's like blowing up a hot dog shaped ballon where it expands near your mouth first and then keeps expanding out towards the tip as you blow more. Similarly, that ring or belt is going to form initially, given the pressure is high enough to deform the brass, at the head and into the unsupported space of the feed cone. And as the pressure wave propagates towards the shoulder, it will reach the areas where the case wall is supported by the chamber walls. And thus, no more belt formation.
Furthermore, in every pic I look at, the ring or belt is in a consistent spot. This is speculation only but it seems this will be hard to get that consistent if the breach is opening early.
So with all this, I still think that the ring or belt is simply the shape of the unsupported feed cone area. And it happens when the pressure is high enough to permanently deform the brass.
Another thing is that Alexander himself pointed out again that the feed cone shape matters. And there are some supporting posts stating that some barrels (I think Odin) show more of a ring than others.
And I'm still not convinced that early bolt release matters. If you think about powder ignition, it's going to literally start burning right at the primer, right there at the head first. Pressure will be the highest there, relative to the shoulder end. And that pressure is going to expand the brass there at the head more than at the shoulder. And as the powder continues to burn there will be a high pressure front that moves with it and continue towards the shoulder. It's like blowing up a hot dog shaped ballon where it expands near your mouth first and then keeps expanding out towards the tip as you blow more. Similarly, that ring or belt is going to form initially, given the pressure is high enough to deform the brass, at the head and into the unsupported space of the feed cone. And as the pressure wave propagates towards the shoulder, it will reach the areas where the case wall is supported by the chamber walls. And thus, no more belt formation.
Furthermore, in every pic I look at, the ring or belt is in a consistent spot. This is speculation only but it seems this will be hard to get that consistent if the breach is opening early.
So with all this, I still think that the ring or belt is simply the shape of the unsupported feed cone area. And it happens when the pressure is high enough to permanently deform the brass.