It shows that things significant to the outcome are happening BEFORE brass is mashed to chamber walls. You could dent your brass in and fire it to see similar. Same brass weight, same chamber.
You can change velocity with dies, and unsized new brass velocity will usually be higher than fireformed brass(sized or not), even though brass weight hasn't changed.
These things are causing INITIAL confinement & load density changes, and they do affect MV and barrel timing for many, even though the same brass will eventually expand to the same chamber.
That weighed FL sized brass shoots well enough, does not mean specific things can be generalized, just to make it so. There are too many contributors to do this.
The test I proposed affects only relative load density, and would not cause change with a compressed load. --I should have qualified that--
I believe it indicates whether a combination would be significantly influenced by load density variances, or not.
As implied, many combinations could be immune to this, while others are sensitive to it. I've tested what I shoot, and not a full gamut of combinations by any means.
As far as same brass weight mashing to same chamber volume, I don't believe that is happening. Magnum cases especially provide for weight variance -that does not contribute to capacity, regardless of chamber(like the belt and large rim & extraction groove).
But I think(a theory) that it may not even matter with magnums, considering their broad pressure curve.
Mid-size cases, even running faster powder, still take a bit of time to fully fit a chamber with any clearances. Any amount of time variance, confinement variance, influences powder burn rate and the pressure peak. These cartridges still do not burn all the powder in a barrel anyway, so pressure peak timing is very significant to outcome as less likely normalized further down the bores.
Underbore cartridges really shine with very high pressures. Not so much otherwise.
This works great, they completely burn up very fast powders even faster due to pressure. A glitch in their pressure curve due to initial confinement, or pretty much anything else, is insignificant as they're running flat against a wall of diminished returns anyway.
The great work-around.
This approach is viable with powder availability & capacity that provides for it, -with enough barrel steel around the chambers.
So far max capacity for this seems to be with the 6.5x47L, but time will really tell.
Larger diameter tennons will be needed to go further up with this to to 28 or 30cal.
