I mean i would say it wouldn't since its an organic material like the sandvich and would be a bad choice for an australium (Robo sandvich is an exception since its metal), but there really isn't any other option since the cozy camper and darwins can't be strange, the razorback can but who would even use it and technically the cleaners carbine could be but it would be too similar to the stock smg. Jarate is really the only option for a good new australium sniper secondary and you could make the jar golden i guess.

You could say that throwing it at someone would coat them in Australium, but that wouldn't be lore accurate since Australium technically has life-extending properties and can make people busted as hell, so it wouldn't make sense. You could probably say though that the sniper just puts gold in a liquid form into his jar (don't expect me to explain how that is/isn't physically possible) and that throwing the gold at someone coats them in said gold, slowing them down. In terms of how it would do the mini-crits, just ask the same question on how does covering someone in piss (urine if it gets censored for some reason) get you free mini-crits.

Sniper got an aussie sniper rifle, but he tripped and ate his gun. Now his Jarate just looks like that.