Mine was doing the same thing but packing my pellet tray up, helped pellet transfer into the breech without stepping up, which had to have been damaging the heads.
I subsequently moved from JSB exact 4.53 to Mossies and the groups tightened and fliers calmed down.
Mine wasn't as good with JSB in 4.52 head size. Don't ask me to explain but I could have shown you.
Do you want any 4.53 to try in yours?