How available are rifles in these calibers? With the infamous Aussie gun restrictions it seems it may be difficult to get them. The other issue is ammo. Are you planning on rolling your own? Is ammo commercially available? WHat is the likelyhood the government will put restrictions on such "sniper" ammo?
In life, strive to take the high road....It offers a better field of fire.
"Robo is right" Fuzzball