The GP11 Swiss stuff is very nice, very accurate, and one goal of handloading is to match the accuracy of the GP11. Unfortunately, the GP11 is Berdan primed, which requires a little research and investment to reload.
Prvi Partizan, Hornady, and Norma all use Boxer primers, and I hear (but cannot confirm) that the Wolf uses good brass, maybe Prvi Partizan manufacture.
Everybody makes a .30 bullet. Best results seem to come from the 160 - 175 range, with the Sierra 168 HPBT usually a prime contender. I'm just working up my kit to reload this stuff myself, enjoying shooting up ammo for the brass.
IMR 4064, 4350 often used. I'm trying the 4064 and RL15 myself with the 168 Sierras.
Both RCBS and Redding make dies, as does Lee, so once you get set up you're good to go.
BTW, current dies reflect sizing for the K31 rather than the older 7.5 chambers, which are slightly different. swissrifles.com has good info on this in the archives.
Regards,
Rick