Just bought a Merkel 160 in 9.3x74. Other than NEI and Mt. Moulds making one, which I have no idea how to design, does anyone else make a mould ( around 280 gr ) for this caliber?

A long time ago, Lyman made a mould in the 260 grain range. I use one that I picked up on EBay. It works well in my drilling, but will the best I've been able to do in my Chapuis is about five inch groups at fifty yards.
Bfly

I sent NEI a woodleigh solid and said I wanted a mold with the same profile. 2 thou fatter in the shank, two lube grooves and a gas check and that is what I got (about 15 years back via a friend at the US Embassy - and you thought it was mail in the diplomatic bag )

Been very happy with it. 275-284grns depending on aloy

Here's one : Lyman 366408.