I'd be astonished if you found "published" data for that cartridge/bullet/powder combination. In cases like this you need to interpolate. Here's what's known:
9.3X57 - case capacity is approx 64.29 grs of H2O
358 Win - case capacity is approx 57.56 grs of H2O
Hodgdon publishes a load for the 358 Win for a 250 gr bullet and SR4759 as follows: 26.0 grs SR4759 - 1845 fps - 51.4K CUP
We know that the same load in your 9.3X57 would produce substantially less pressure, since the cartridge has more capacity and the bore is greater in size, so it would be "safe" in a firearm that is designed for 51.4K CUP. You want to use a heavier 280 gr bullet, so that offsets the pressure decrease. You have some choices:
- buy a 250 gr bullet (gas-checked), and load in the 20.0 to 26.0 gr range;
- use the 280 gr bullet (gas-checked) and load in a lower range, e.g. 18.0 to 24.0 grs;
- keep looking for published loads or waiting for them to be produced; or
- run away screaming and buy a different gun.
If it was me (and I would like to buy a 9.3X57 some day), I'd go no higher than 250 grs, and if I used that powder, I'd load in the 22.0 to 28.0 gr range and stop at 1800 fps, whatever comes first. With the 280 gr, I'd use 20.0 to 26.0 grs and stop at 1700 fps.
As "Sanity Checks":
1.
"Cartridges of the World" 10th Edition has loads for both the 9X57 and 9.3X57 as follows:
9X57 - 280 gr - 43.0 grs IMR-3031 - 2030 fps
9.3X57 - 286 gr - 43.0 grs IMR-3031 - 2070 fps
That's almost twice as much of a slower powder to produce what should be pretty much a top MV for a 280 gr bullet.
2.
AND from "Gunboards"
http://forums.gunboards.com/showthread.php?645-Handloading-the-9-3x57
3.
AND from "Cast Boolits"
http://castboolits.gunloads.com/showthread.php?162351-280-gr-cast-bullet-loads-9-3x57
"A load that I use for general practice is 23.0 gr of SR 4759 Win Lg Rifle primer. Vel in my rifle is 1506 fps and accuracy is excellent. My bullet is the NOE 290gr. 45.5 gr of Varget will get 2036 fps. These loads are safe in my rifle, use at your own risk."
