In the Northern Territory at least, and I thought the whole of Australia, black powder firearms escaped the "nothing over .38" restriction. I don't shoot with the Black Powder club, but would be interested to know if BP cartridge guns over .38 (or over .45 for that matter) can still be used during an official event. If so, that would provide a legitimate reason for pretty-well anyone with an H-class licence in Australia, with the ability to meet BP club-attendance minimums.

In the NT, firearms manufactured before 1900 can be held fairly freely on a special 'Antique Licence', and discharged under certain circumstances, such as at Collectors' Shoots. Generally a re-barrel would not be regarded as changing the date of manufacture of the firearm, especially if it was rebarrelled to an obsolete 'period' cartridge like the Snider.

I should add that the Antique Licence covering H-class might be difficult to get unless a normal H-class Collectors Licence was already held. The NT Coppers tend to have a "no dickheads" policy when it comes to this sort of thing. Matter of fact, so do the rest of us shooters!