my own limited knowledge and frame hits, I found thicker bands and heavier ammo lead to inaccuracy due to my wrists being like Larry graysons, a lighter setup. 65 bands and 9.5mm steel cured it.
good luck with him, I have never had a dog only bitches, when I bought the whippet there was a cracking Pied dog pup, I was very tempted but stuck with a bitch pup, I sometimes think I may be missing out sometimes.
thought the whippet had got her first hare, to be fair she has only run around four, off the ditch on winter wheat, 3 tight turns and I thought she's got it this time, as they got to the tree everything stopped, Hartley had disappeared into it