Re: 22-250 projectile size
There are no laws that dictate the weights of bullets in Australia. In the UK, Europe and USA there are laws that dictate the caliber and Wt of projectiles used to take different game. Here there are no such rules. We do not have 'game' animals as such. Just feral and native. Unprotected and protected.
You just use whatever your rifle shoots well with and will take the animal cleanly.
IE; .224 55gn Hornady SX in my .223 for foxes and rabbits. .243 90gn Sierra SP for roos. .358 200gn Hornady FX in the Whelen for pigs.
I dont try to use .224 53gn Sierra boat tailed match hollow points for foxes. I dont use the 55gn .224s on roos either as they will blow up on fore arms and badly wound a roo.
Up to you what you use.