(Same problem in my cricket)I have found this in other forum:
I have found the problem with indexing of cricket magazines is down to the indexing cam bending upwards, when these parts are cut out with the EDM machine the cut left where the wire has gone in to cut the pin hole closes up causing the tip of the cam to move upwards, so when you cock the gun the indexing cam doesn't move far enough down to align the next pellet, I have had 4 people come with the same fault, my solution to this problem is to put the gap so the 2 sides are parallel to each other and then fill the gap with silver solder to prevent the gap closing up again.