Hello buckstix - the 9.3x62 is such a marvelous ctg., the only problems being a lack of good cup and core bullets here in NA.
Some time back I worked up loads for the 285gr. Speer Grand Slam in my old Oberndorf Mauser. I am sure that 285gr. is likely a great bullet, but I've not seen them for many years. I simply used .30/06 and yes, they are a bit small in the head. I used that brass for 40 years and it's still fine, although I did not treat is like a varmint round- likely no more than 6 or 8 rounds each.

I worked up loads back in the 80's for it, along with the (too soft imho) Speer 270gr. using BLC2.

Seems to me, Steve Szihn also played with this round these bullets and BLC2 as well with similar results.

Years later, when Hodgdon came out with it's Annual Manual I found those loads(almost) listed for the 9.3x62, however their ballistics were a mite slower than mine.

I was able to see 2,675fps with the 270gr. and 2,519fps with the 285's with seemingly normal pressures. In weighing cases empty and then full of water, I found my formed brass to hold 78gr. water. This is considerably more than a standard improved .30/06 case.

Many people do not realize just how good the 9.3x62 can be, when used in a good action.