First bet is leading.
Second is inconsistency in the way the gun is rested.
Wiping may help, but with the duplex shouldn't be needed and using a wiping technigue that doesn't agree with the duplex load could make for a much larger mess. Maybe try something like a slightly damp (mpro7 etc) 2 1/2 in. flannel patch pushed thru the bore on a nylon brush in place of a jag.
3rd, just flat could be the rifle doesn't like the load, maybe to much crimp, maybe adjustments in both of the powder charges? try a harder alloy.
Lastly it is seldom that two separate shooters will shoot to the same point of aim with the same rifle, happens occasionally but not something you can count on.
