Re: Case design
I presume that you mean 9.3 x 62.
Producing a wildcat can be one of the most satisfying things that a hunter/shooter can do. We don't need any reason other than 'I want to...' to send us off in pursuit of a design, all the while thowing tidy sums of cash into the mix simply because there isn't anything standard or off-the-shelf that we can make work correctly. I'm with you on this, BTDT.
But...(and if you've already done this, ignore me) take a look at:
6.5 X 68S
6.5-06 Ackley Improved
6.5 x 64 Brenneke
6.5 x 65 RWS
6.5 Rem. Mag.
With exception of the 6.5 Rem. Mag., these are all basically what you are trying to get to without a lot of necking down, neck turning (or reaming) and all of the custom stuff that goes along with a project like this. They all have gently sloping shoulders that beg to be improved and in fact the 6.5-06 AI and the 6.5 Gibbs obviously have already been through the process. The 264 Hawk is close to that. They all have case capacities of 68 gr. to 86 gr. of water. So why beat yourself up making cases the hard way?
The angle of the shoulder should work in conjunction with the length of the neck to curtail throat erosion. It's when the plasma gets directed right at the sides of the throat that a great deal of erosion takes place. The idea is to channel the plasma straight down the bore or get it to impinge on the inside of the neck before it hits the throat.
Unburned, long grain powder has a definite negative effect on the throat of a chamber. It acts like sandblasting by scrubbing the surface of both the throat and the bore. The heat of the plasma does enough damage without adding the scrubbing on top of that. The effect of steep shoulders is that the powder gets delayed slightly in the case, allowing more of it to burn in the case as opposed to on the way down the barrel.