When I first got an EV2, I noticed about one shot in ten would be a flyer with the batch of JSBs i had which was mega in the HW100 I'd been using for 4 years. When pellet testing it at 50m indoors, I noticed super tight groups which were spoiled by the odd flyer, shooting at the Bisley 10m paper air rifle targets I could easily see the holes made by the pellets in the tight groups were perfectly round, but the flyers were elongated as if the pellets were tumbling. The rifle was an Ostler EV2 with a CZ match barrel. I didn't have any other batches with me that day but other batches were fine since then. I've no idea what the cause of the tumbling was, maybe just a crap batch, but I speculated that maybe the barrel had a slow twist rate and the pellets started to wobble around 45-50 yards.
I think given the drop for 12 ft.lbs .177 at 55 yards where the pellets are descending. If they are spin stabiised they will still be pointing in the same direction as at the muzzle.. If they are drag stabilised they will be pointing slightly down, like a shuttlecock atoward the end of its flit. I wonder if at that sort of range they may be in a transition from mostly spin-stabilised to mostly drag-stabilised, this could be a cause of instability creeping in at certain ranges. Unless or until we could film them in flight with super high speed, high res cameras, I don't think it's likely we'll ever know for sure.