May be that they're a little too big for the Swiss rifle. Not often, but sometimes cast bullets will shoot better when they're smaller. I see it with my .223 with many different bullets and loads. Those K31s have pretty tight bores, and mine at least works best with bullets no bigger than .309. If you have a .308 or .309 die you might try running some through that and trying again. Might try putting some tumble lube on them as well to see what that does. BTW, those K31s make wonderful cast bullet rifles! Mine is incredibly accurate with the Lee c-312-155-2R sized to .3085 over pretty much any powder I want to use at 2000 fps. Best with IMR 4895 and Varget.