Greetings from a fellow Notts - er! (I just invented a word!)
Stick to rabbits and woodies (edible, commonly available and easily identified), but for 'fun' magpies and crows don't sit still too long, so provide a more difficult target, provided you can dispose of them !
I've been known to use mine quite close to houses sometimes, as they make very little noise and are easily pocketed.
I prefer to use 10mm ball bearings or glass marbles, but like most things, it's a personal choice - just have fun !!