I've seen a tool to up-size a pellet. The tool consists of 2 steel plates that slide against one another and has a half pellet profile on each plate. The starting point is standard sized to the pellet it's used on, but the 2 grooves get very minutely wider and shorter towards the other end. The pellet is placed against one plate and the other plate is slid past along the groove. The pellet rolls round and down the fixed plate until the moving plate slides past and out the back pops the pellet. It is said to make the head, waist, and skirt concentric. Remember this is 20 years ago with a Barracuda pellet, but 50 yard groups went from 3/4" down to 3/8" with a GC2 shooting from a fixture and in a tunnel. The maker was a tinkerer and all he did was shoot groups in his tunnel and try to improve them. Forgot to mention the groups were 25 shots. I didn't witness this myself, but several others I shoot with have confirmed. The sizing roller I have seen and it works.