Hello all!
I have a ZKK602 in 458WinMag which doesn´t feed well with short bullets (not uncommon i´ve heard).
When loading for ex.Hornady 350gr RN bullets i have two crimping canelures on the bullet 1/4" apart. If i crimp in the rear canelure the gun feeds flawlessly but I have then increased the space available for powder.
Can I still use the minimum loads listed or should I adjust my loads? If so how much?

Personally I've always crimped in the rear cannelure on .458 bullets. I use the 405gr Rem JFP for my plinking load and crimp it in the rear cannelure for my .458 Win's and have had no trouble.

I've loaded the 350 gr bullets to 458 win mag levels in the 458 Lott and they perform fine. I wouldn't worry about the slightly increased case capacity.

I load the Hornady 350 over 76.0 H-322 with a Federal 215 primer. Have tried it both ways in my Ruger No. 1 .458 WM. Crimping in the front is well under minimum OAL and is a compressed load, but other than flat primers, no pressure signs - no rings, primer backflow or back-out. Seating to the rear groove also flattens the primer, rifle shoots to the same POI at 100 yards, velocity the same (2550), and you can hear powder rattling in the case. I have not tested the longer load enough yet to see if the space will cause inconsistent pressure and velocity, but the shorter compressed load is very consistent.
I originally used the shorter load as earlier lots of Hornady 350's I bought had only the 1 groove. Later lots have both, so I am testing the longer load to decrease pressures (though it has not been a problem). So far, no performance difference noted.
Hope this helps.
Jason