How many shots per each powder charge ? Did you clean the bore at any point in the testing ? seems as the groups started to open up after the 4th load fired with the H335 which may be in part due to barrel fouling. What about the heat of the barrel ? did you allow sufficient cooling time between rounds ?
I would ask what the outside temps were but this is where the H322 should have had the edge over the H335 as the H322 is one of the extreme rated powders from Hodgdon. Less temperature sensitive.